diff --git a/crates/rle/Cargo.toml b/crates/rle/Cargo.toml
index 5384fc4a..2aa73a86 100644
--- a/crates/rle/Cargo.toml
+++ b/crates/rle/Cargo.toml
@@ -6,7 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-bumpalo = { version = "3.10.0", features = ["collections"] }
+bumpalo = { version = "3.10.0", features = ["collections", "boxed"] }
 num = "0.4.0"
 enum-as-inner = "0.5.1"
 owning_ref = "0.4.1"
diff --git a/crates/rle/src/lib.rs b/crates/rle/src/lib.rs
index 8d1cf1ec..9bbdf923 100644
--- a/crates/rle/src/lib.rs
+++ b/crates/rle/src/lib.rs
@@ -1,3 +1,4 @@
+#![allow(unused)]
 //! Run length encoding library.
 //!
 //! There are many mergeable types. By merging them together we can get a more compact representation of the data.
diff --git a/crates/rle/src/rle_tree.rs b/crates/rle/src/rle_tree.rs
index 4d62f3a4..0755de14 100644
--- a/crates/rle/src/rle_tree.rs
+++ b/crates/rle/src/rle_tree.rs
@@ -1,3 +1,4 @@
+pub(self) use bumpalo::boxed::Box as BumpBox;
 pub(self) use bumpalo::collections::vec::Vec as BumpVec;
 use owning_ref::OwningRefMut;
 use std::marker::{PhantomData, PhantomPinned};
@@ -8,6 +9,7 @@ use tree_trait::RleTreeTrait;
 
 use self::node::{InternalNode, Node};
 
+mod fixed_size_vec;
 mod node;
 mod tree_trait;
 
@@ -23,11 +25,11 @@ pub struct RleTreeRaw<'a, T: Rle, A: RleTreeTrait<T>> {
 type TreeRef<T, A> =
     OwningRefMut<Box<(Box<Bump>, RleTreeRaw<'static, T, A>)>, RleTreeRaw<'static, T, A>>;
 
-pub struct RleTreeCreator<T: Rle + 'static, A: RleTreeTrait<T> + 'static> {
+pub struct RleTree<T: Rle + 'static, A: RleTreeTrait<T> + 'static> {
     tree: TreeRef<T, A>,
 }
 
-impl<T: Rle + 'static, A: RleTreeTrait<T> + 'static> RleTreeCreator<T, A> {
+impl<T: Rle + 'static, A: RleTreeTrait<T> + 'static> RleTree<T, A> {
     pub fn new() -> Self {
         let bump = Box::new(Bump::new());
         let tree = RleTreeRaw::new(unsafe { &*(&*bump as *const _) });
@@ -50,30 +52,38 @@ impl<'a, T: Rle, A: RleTreeTrait<T>> RleTreeRaw<'a, T, A> {
     fn new(bump: &'a Bump) -> Self {
         Self {
             bump,
-            node: Node::Internal(InternalNode::new(bump)),
+            node: Node::Internal(BumpBox::new_in(InternalNode::new(bump, None), bump)),
             _pin: PhantomPinned,
             _a: PhantomData,
         }
     }
 
-    fn insert(&mut self, index: A::Int, value: T) {
-        self.node.insert(index, value);
+    #[inline]
+    pub fn insert(&mut self, index: A::Int, value: T) {
+        match self.node {
+            Node::Internal(ref mut node) => {
+                node.insert(index, value);
+            }
+            _ => {
+                unreachable!()
+            }
+        }
     }
 
     /// return a cursor to the tree
-    fn get(&self, index: A::Int) {
+    pub fn get(&self, index: A::Int) {
         todo!()
     }
 
-    fn iter(&self) {
+    pub fn iter(&self) {
         todo!()
     }
 
-    fn delete_range(&mut self, from: A::Int, to: A::Int) {
+    pub fn delete_range(&mut self, from: A::Int, to: A::Int) {
         todo!()
     }
 
-    fn iter_range(&self, from: A::Int, to: A::Int) {
+    pub fn iter_range(&self, from: A::Int, to: A::Int) {
         todo!()
     }
 
@@ -91,29 +101,35 @@ fn test() {
 
     struct Trait;
     impl RleTreeTrait<Range<usize>> for Trait {
+        const MAX_CHILDREN_NUM: usize = 4;
         type Int = usize;
         type InternalCache = ();
 
-        fn update_cache() {
-            todo!()
-        }
-
-        fn min_children() -> usize {
-            5
-        }
-
-        fn before_insert_internal(_: InternalNode<'_, Range<usize>, Self>) {
-            todo!()
-        }
-
         fn find_insert_pos_internal(
-            _: InternalNode<'_, Range<usize>, Self>,
+            _: &mut InternalNode<'_, Range<usize>, Self>,
             _: Self::Int,
         ) -> usize {
             todo!()
         }
+
+        const MIN_CHILDREN_NUM: usize = Self::MAX_CHILDREN_NUM / 2;
+
+        fn update_cache_leaf(node: &mut node::LeafNode<'_, Range<usize>, Self>) {
+            todo!()
+        }
+
+        fn update_cache_internal(node: &mut InternalNode<'_, Range<usize>, Self>) {
+            todo!()
+        }
+
+        fn find_insert_pos_leaf(
+            node: &mut node::LeafNode<'_, Range<usize>, Self>,
+            index: Self::Int,
+        ) -> (usize, usize) {
+            todo!()
+        }
     }
-    let mut t: RleTreeCreator<Range<usize>, Trait> = RleTreeCreator::new();
+    let mut t: RleTree<Range<usize>, Trait> = RleTree::new();
     let tree = t.get_mut();
     tree.insert(10, 0..5);
 }
diff --git a/crates/rle/src/rle_tree/fixed_size_vec.rs b/crates/rle/src/rle_tree/fixed_size_vec.rs
new file mode 100644
index 00000000..6cd5516c
--- /dev/null
+++ b/crates/rle/src/rle_tree/fixed_size_vec.rs
@@ -0,0 +1,52 @@
+use super::Bump;
+use super::BumpVec;
+use std::marker::PhantomPinned;
+use std::ops::Deref;
+use std::ops::DerefMut;
+
+#[derive(Debug)]
+pub(super) struct FixedSizedVec<'a, T> {
+    data: BumpVec<'a, T>,
+    _pin: PhantomPinned,
+}
+
+impl<'a, T> FixedSizedVec<'a, T> {
+    #[inline]
+    pub(super) fn with_capacity(capacity: usize, bump: &'a Bump) -> Self {
+        Self {
+            data: BumpVec::with_capacity_in(capacity, bump),
+            _pin: PhantomPinned,
+        }
+    }
+
+    #[inline]
+    pub(super) fn push(&mut self, value: T) {
+        debug_assert!(self.data.len() < self.data.capacity());
+        self.data.push(value);
+    }
+
+    #[inline]
+    pub(super) fn insert(&mut self, index: usize, value: T) {
+        debug_assert!(self.data.len() < self.data.capacity());
+        self.data.insert(index, value);
+    }
+
+    #[inline]
+    pub(super) fn pop(&mut self) -> Option<T> {
+        self.data.pop()
+    }
+}
+
+impl<'a, T> Deref for FixedSizedVec<'a, T> {
+    type Target = [T];
+
+    fn deref(&self) -> &Self::Target {
+        &self.data
+    }
+}
+
+impl<'a, T> DerefMut for FixedSizedVec<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.data
+    }
+}
diff --git a/crates/rle/src/rle_tree/node.rs b/crates/rle/src/rle_tree/node.rs
index 0a1113f7..b9a357cf 100644
--- a/crates/rle/src/rle_tree/node.rs
+++ b/crates/rle/src/rle_tree/node.rs
@@ -1,8 +1,14 @@
-use std::marker::{PhantomData, PhantomPinned};
+use std::{
+    marker::{PhantomData, PhantomPinned},
+    pin::Pin,
+    ptr::NonNull,
+};
 
 use crate::Rle;
 
-use super::{tree_trait::RleTreeTrait, BumpVec, RleTreeRaw};
+use super::{
+    fixed_size_vec::FixedSizedVec, tree_trait::RleTreeTrait, BumpBox, BumpVec, RleTreeRaw,
+};
 use bumpalo::Bump;
 use enum_as_inner::EnumAsInner;
 mod internal_impl;
@@ -10,15 +16,16 @@ mod leaf_impl;
 
 #[derive(Debug, EnumAsInner)]
 pub enum Node<'a, T: Rle, A: RleTreeTrait<T>> {
-    Internal(InternalNode<'a, T, A>),
-    Leaf(LeafNode<'a, T, A>),
+    Internal(BumpBox<'a, InternalNode<'a, T, A>>),
+    Leaf(BumpBox<'a, LeafNode<'a, T, A>>),
 }
 
 #[derive(Debug)]
 pub struct InternalNode<'a, T: Rle, A: RleTreeTrait<T>> {
     bump: &'a Bump,
-    parent: Option<&'a InternalNode<'a, T, A>>,
-    children: BumpVec<'a, Node<'a, T, A>>,
+    parent: Option<NonNull<InternalNode<'a, T, A>>>,
+    children: FixedSizedVec<'a, Node<'a, T, A>>,
+    cache: A::InternalCache,
     _pin: PhantomPinned,
     _a: PhantomData<A>,
 }
@@ -26,19 +33,20 @@ pub struct InternalNode<'a, T: Rle, A: RleTreeTrait<T>> {
 #[derive(Debug)]
 pub struct LeafNode<'a, T: Rle, A: RleTreeTrait<T>> {
     bump: &'a Bump,
-    parent: &'a InternalNode<'a, T, A>,
-    children: BumpVec<'a, T>,
-    prev: Option<&'a LeafNode<'a, T, A>>,
-    next: Option<&'a LeafNode<'a, T, A>>,
+    parent: NonNull<InternalNode<'a, T, A>>,
+    children: FixedSizedVec<'a, T>,
+    prev: Option<NonNull<LeafNode<'a, T, A>>>,
+    next: Option<NonNull<LeafNode<'a, T, A>>>,
     _pin: PhantomPinned,
     _a: PhantomData<A>,
 }
 
 impl<'a, T: Rle, A: RleTreeTrait<T>> Node<'a, T, A> {
-    pub(super) fn insert(&mut self, index: A::Int, value: T) {
-        match self {
-            Node::Internal(node) => {}
-            Node::Leaf(node) => {}
-        }
+    fn new_internal(bump: &'a Bump) -> Self {
+        Self::Internal(BumpBox::new_in(InternalNode::new(bump, None), bump))
+    }
+
+    fn new_leaf(bump: &'a Bump, parent: NonNull<InternalNode<'a, T, A>>) -> Self {
+        Self::Leaf(BumpBox::new_in(LeafNode::new(bump, parent), bump))
     }
 }
diff --git a/crates/rle/src/rle_tree/node/internal_impl.rs b/crates/rle/src/rle_tree/node/internal_impl.rs
index 68db1e2f..7f786cc0 100644
--- a/crates/rle/src/rle_tree/node/internal_impl.rs
+++ b/crates/rle/src/rle_tree/node/internal_impl.rs
@@ -1,13 +1,74 @@
 use super::*;
 
 impl<'a, T: Rle, A: RleTreeTrait<T>> InternalNode<'a, T, A> {
-    pub fn new(bump: &'a Bump) -> Self {
+    pub fn new(bump: &'a Bump, parent: Option<NonNull<Self>>) -> Self {
         Self {
             bump,
-            parent: None,
-            children: BumpVec::with_capacity_in(A::max_children(), bump),
+            parent,
+            children: FixedSizedVec::with_capacity(A::MAX_CHILDREN_NUM, bump),
+            cache: Default::default(),
             _pin: PhantomPinned,
             _a: PhantomData,
         }
     }
+
+    #[inline]
+    fn _split(&mut self) -> Self {
+        let mut ans = Self::new(self.bump, self.parent);
+        for i in 0..A::MIN_CHILDREN_NUM {
+            ans.children.push(self.children.pop().unwrap());
+        }
+
+        ans
+    }
+
+    pub fn insert(&mut self, index: A::Int, value: T) -> Result<(), Self> {
+        if self.children.len() == 0 {
+            debug_assert!(self.parent.is_none());
+            let ptr = NonNull::new(self as *mut _).unwrap();
+            self.children.push(Node::new_leaf(self.bump, ptr));
+            return Ok(());
+        }
+
+        let insert_pos = A::find_insert_pos_internal(self, index);
+        let child = &mut self.children[insert_pos];
+        let new = match child {
+            Node::Internal(child) => {
+                if let Err(new) = child.insert(index, value) {
+                    let new = Node::Internal(BumpBox::new_in(new, self.bump));
+                    Some(new)
+                } else {
+                    None
+                }
+            }
+            Node::Leaf(child) => {
+                if let Err(new) = child.insert(index, value) {
+                    let new = Node::Leaf(BumpBox::new_in(new, self.bump));
+                    Some(new)
+                } else {
+                    None
+                }
+            }
+        };
+
+        if let Some(new) = new {
+            if self.children.len() == A::MAX_CHILDREN_NUM {
+                let mut ans = self._split();
+                if insert_pos <= self.children.len() {
+                    self.children.insert(insert_pos, new);
+                } else {
+                    ans.children.insert(insert_pos - self.children.len(), new);
+                }
+
+                A::update_cache_internal(self);
+                A::update_cache_internal(&mut ans);
+                return Err(ans);
+            }
+
+            self.children.insert(insert_pos, new);
+            A::update_cache_internal(self);
+        }
+
+        Ok(())
+    }
 }
diff --git a/crates/rle/src/rle_tree/node/leaf_impl.rs b/crates/rle/src/rle_tree/node/leaf_impl.rs
index 5109bc4c..9b7729b0 100644
--- a/crates/rle/src/rle_tree/node/leaf_impl.rs
+++ b/crates/rle/src/rle_tree/node/leaf_impl.rs
@@ -1,15 +1,117 @@
 use super::*;
 
 impl<'a, T: Rle, A: RleTreeTrait<T>> LeafNode<'a, T, A> {
-    pub fn new(bump: &'a Bump, parent: &'a InternalNode<'a, T, A>) -> Self {
+    #[inline]
+    pub fn new(bump: &'a Bump, parent: NonNull<InternalNode<'a, T, A>>) -> Self {
         Self {
             bump,
             parent,
-            children: BumpVec::with_capacity_in(A::max_children(), bump),
+            children: FixedSizedVec::with_capacity(A::MAX_CHILDREN_NUM, bump),
             prev: None,
             next: None,
             _pin: PhantomPinned,
             _a: PhantomData,
         }
     }
+
+    #[inline]
+    fn _split(&mut self) -> Self {
+        let mut ans = Self::new(self.bump, self.parent);
+        for i in 0..A::MIN_CHILDREN_NUM {
+            ans.children.push(self.children.pop().unwrap());
+        }
+        ans.next = self.next;
+        ans.prev = Some(NonNull::new(self).unwrap());
+        self.next = Some(NonNull::new(&mut ans).unwrap());
+        ans
+    }
+
+    pub fn push_child(&mut self, value: T) -> Result<(), Self> {
+        if self.children.len() > 0 {
+            let last = self.children.last_mut().unwrap();
+            if last.is_mergable(&value, &()) {
+                last.merge(&value, &());
+                A::update_cache_leaf(self);
+                return Ok(());
+            }
+        }
+
+        if self.children.len() == A::MAX_CHILDREN_NUM {
+            let mut ans = self._split();
+            ans.push_child(value);
+            A::update_cache_leaf(self);
+            A::update_cache_leaf(&mut ans);
+            return Err(ans);
+        }
+
+        self.children.push(value);
+        A::update_cache_leaf(self);
+        Ok(())
+    }
+
+    pub fn insert(&mut self, raw_index: A::Int, value: T) -> Result<(), Self> {
+        if self.children.len() == 0 {
+            self.children.push(value);
+            return Ok(());
+        }
+
+        let (mut index, mut offset) = A::find_insert_pos_leaf(self, raw_index);
+        let prev = if offset == 0 {
+            Some(&mut self.children[index - 1])
+        } else if offset == self.children[index].len() {
+            index += 1;
+            offset = 0;
+            Some(&mut self.children[index - 1])
+        } else {
+            None
+        };
+
+        if let Some(prev) = prev {
+            // clean cut, should no split
+            if prev.is_mergable(&value, &()) {
+                prev.merge(&value, &());
+                A::update_cache_leaf(self);
+                return Ok(());
+            }
+
+            if self.children.len() == A::MAX_CHILDREN_NUM {
+                let mut ans = self._split();
+                if index <= self.children.len() {
+                    self.children.insert(index, value);
+                } else {
+                    ans.children.insert(index - self.children.len(), value);
+                }
+
+                A::update_cache_leaf(self);
+                A::update_cache_leaf(&mut ans);
+                return Err(ans);
+            } else {
+                self.children.insert(index, value);
+                A::update_cache_leaf(self);
+                return Ok(());
+            }
+        }
+
+        // need to split child
+        let a = self.children[index].slice(0, offset);
+        let b = self.children[index].slice(offset, self.children[index].len());
+        self.children[index] = a;
+
+        if self.children.len() == A::MAX_CHILDREN_NUM {
+            let mut ans = self._split();
+            if index < self.children.len() {
+                self.children.insert(index + 1, b);
+            } else {
+                ans.children.insert(index - self.children.len() + 1, b);
+            }
+
+            A::update_cache_leaf(self);
+            A::update_cache_leaf(&mut ans);
+            return Err(ans);
+        }
+
+        self.children.insert(index + 1, value);
+        A::update_cache_leaf(self);
+        Ok(())
+    }
 }
diff --git a/crates/rle/src/rle_tree/tree_trait.rs b/crates/rle/src/rle_tree/tree_trait.rs
index 67012abb..2bbc10f7 100644
--- a/crates/rle/src/rle_tree/tree_trait.rs
+++ b/crates/rle/src/rle_tree/tree_trait.rs
@@ -1,19 +1,19 @@
+use std::fmt::Debug;
+
 use crate::Rle;
 
-use super::node::{InternalNode, Node};
+use super::node::{InternalNode, LeafNode, Node};
 
 pub trait RleTreeTrait<T: Rle>: Sized {
-    type Int: num::Integer;
-    type InternalCache;
+    const MAX_CHILDREN_NUM: usize;
+    const MIN_CHILDREN_NUM: usize = Self::MAX_CHILDREN_NUM / 2;
+    type Int: num::Integer + Copy;
+    type InternalCache: Default + Debug;
 
-    fn update_cache();
-    fn min_children() -> usize;
-
-    #[inline]
-    fn max_children() -> usize {
-        Self::min_children() * 2
-    }
-
-    fn before_insert_internal(node: InternalNode<'_, T, Self>);
-    fn find_insert_pos_internal(node: InternalNode<'_, T, Self>, index: Self::Int) -> usize;
+    fn update_cache_leaf(node: &mut LeafNode<'_, T, Self>);
+    fn update_cache_internal(node: &mut InternalNode<'_, T, Self>);
+    fn find_insert_pos_internal(node: &mut InternalNode<'_, T, Self>, index: Self::Int) -> usize;
+    /// returns (index, offset)
+    /// if 0 < offset < children[index].len(), we need to split the node
+    fn find_insert_pos_leaf(node: &mut LeafNode<'_, T, Self>, index: Self::Int) -> (usize, usize);
 }