diff --git a/src/rstd/collections.rs b/src/rstd/collections.rs
index 579e1a6..73697df 100644
--- a/src/rstd/collections.rs
+++ b/src/rstd/collections.rs
@@ -1,5 +1,6 @@
 //! Standard generic collections.
 
+pub mod avl;
 pub mod pair;
 pub mod rbtree;
 pub mod stack;
diff --git a/src/rstd/collections/avl.rs b/src/rstd/collections/avl.rs
new file mode 100644
index 0000000..8413dc9
--- /dev/null
+++ b/src/rstd/collections/avl.rs
@@ -0,0 +1,165 @@
+use std::{error::Error, fmt::Display, rc::Rc};
+
+use crate::rcore::*;
+use crate::rstd::{
+    atomic::{au64::*, *},
+    nullable::*,
+    point::*,
+};
+
+#[derive(Debug)]
+pub enum TreeParseError<E> {
+    Int(IntParseError),
+    Point(PointParseError),
+    Key(E),
+    LeafHeight(u64),
+    Balance(u64, u64),
+}
+
+impl<E> From<IntParseError> for TreeParseError<E> {
+    fn from(value: IntParseError) -> Self {
+        Self::Int(value)
+    }
+}
+
+impl<E> From<PointParseError> for TreeParseError<E> {
+    fn from(value: PointParseError) -> Self {
+        Self::Point(value)
+    }
+}
+
+impl<E: Display> Display for TreeParseError<E> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Int(int_error) => {
+                f.write_fmt(format_args!("failed to parse AVL tree height: {int_error}"))
+            }
+            Self::Point(point_error) => f.write_fmt(format_args!(
+                "failed to parse AVL node reference: {point_error}"
+            )),
+            Self::Key(key_error) => {
+                f.write_fmt(format_args!("failed to parse AVL node key: {key_error}"))
+            }
+            Self::LeafHeight(height) => {
+                f.write_fmt(format_args!("invalid AVL leaf height: {height}!=0."))
+            }
+            Self::Balance(lh, rh) => f.write_fmt(format_args!("unbalanced AVL node: {lh} {rh}.")),
+        }
+    }
+}
+
+impl<E: Error> Error for TreeParseError<E> {}
+
+struct AvlNode<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> {
+    l: AvlTree<'a, Ctx, A>,
+    r: AvlTree<'a, Ctx, A>,
+    key: Rc<A>,
+}
+
+struct AvlTree<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> {
+    node: Nullable<'a, Ctx, AvlNode<'a, Ctx, A>>,
+    height: u64,
+}
+
+#[derive(Clone)]
+struct AvlNodeFactory<F>(F);
+
+#[derive(Clone)]
+struct AvlTreeFactory<F>(NullableFactory<AvlNodeFactory<F>>);
+
+impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Serializable for AvlNode<'a, Ctx, A> {
+    fn serialize(&self, serializer: &mut dyn Serializer) {
+        self.l.serialize(serializer);
+        self.r.serialize(serializer);
+        self.key.serialize(serializer);
+    }
+}
+
+impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Serializable for AvlTree<'a, Ctx, A> {
+    fn serialize(&self, serializer: &mut dyn Serializer) {
+        self.height.serialize(serializer);
+        self.node.serialize(serializer);
+    }
+}
+
+impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Mentionable<'a, Ctx> for AvlNode<'a, Ctx, A> {
+    type Fctr = AvlNodeFactory<A::Fctr>;
+
+    fn factory(&self) -> Self::Fctr {
+        AvlNodeFactory(self.key.factory())
+    }
+
+    fn points_typed(&self, points: &mut impl TakesPoints<'a, Ctx>) {
+        self.l.points_typed(points);
+        self.r.points_typed(points);
+        self.key.points_typed(points);
+    }
+}
+
+impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Mentionable<'a, Ctx> for AvlTree<'a, Ctx, A> {
+    type Fctr = AvlTreeFactory<A::Fctr>;
+
+    fn factory(&self) -> Self::Fctr {
+        AvlTreeFactory(self.node.factory())
+    }
+
+    fn points_typed(&self, points: &mut impl TakesPoints<'a, Ctx>) {
+        self.node.points_typed(points);
+    }
+}
+
+impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for AvlNodeFactory<F> {
+    type Mtbl = AvlNode<'a, Ctx, F::Mtbl>;
+
+    type ParseError = TreeParseError<F::ParseError>;
+
+    fn deserialize(
+        &self,
+        deserializer: &mut dyn Deserializer,
+        resolver: Rc<dyn Resolver<'a, Ctx>>,
+        addresses: &mut Addresses,
+    ) -> ParseResult<'a, Ctx, Self> {
+        let tree_factory = AvlTreeFactory(NullableFactory::new(self.clone()));
+        let l = tree_factory.deserialize(deserializer, resolver.clone(), addresses)?;
+        let r = tree_factory.deserialize(deserializer, resolver.clone(), addresses)?;
+        if std::cmp::max(l.height, r.height) - std::cmp::min(l.height, r.height) > 1 {
+            return Err(TreeParseError::Balance(l.height, r.height));
+        }
+        let key = self
+            .0
+            .deserialize(deserializer, resolver.clone(), addresses)
+            .map_err(TreeParseError::Key)?
+            .into();
+        Ok(AvlNode { l, r, key })
+    }
+
+    fn unexpected_tail(&self, tail: &[u8]) -> Self::ParseError {
+        TreeParseError::Key(self.0.unexpected_tail(tail))
+    }
+}
+
+impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for AvlTreeFactory<F> {
+    type Mtbl = AvlTree<'a, Ctx, F::Mtbl>;
+
+    type ParseError = TreeParseError<F::ParseError>;
+
+    fn deserialize(
+        &self,
+        deserializer: &mut dyn Deserializer,
+        resolver: Rc<dyn Resolver<'a, Ctx>>,
+        addresses: &mut Addresses,
+    ) -> ParseResult<'a, Ctx, Self> {
+        let node = self.0.deserialize(deserializer, resolver, addresses)?;
+        let height = u64::a_deserialize(deserializer)?;
+        if let Nullable::Null(_) = node {
+            if height != 0 {
+                return Err(TreeParseError::LeafHeight(height));
+            }
+        }
+        Ok(AvlTree { node, height })
+    }
+
+    fn unexpected_tail(&self, tail: &[u8]) -> Self::ParseError {
+        u64::a_unexpected_tail(tail).into()
+    }
+}
diff --git a/src/rstd/collections/rbtree.rs b/src/rstd/collections/rbtree.rs
index 1d7c4d3..f76a71e 100644
--- a/src/rstd/collections/rbtree.rs
+++ b/src/rstd/collections/rbtree.rs
@@ -22,28 +22,27 @@ pub enum TreeParseError<E> {
 
 impl<E> From<BooleanParseError> for TreeParseError<E> {
     fn from(value: BooleanParseError) -> Self {
-        TreeParseError::Boolean(value)
+        Self::Boolean(value)
     }
 }
 
 impl<E> From<PointParseError> for TreeParseError<E> {
     fn from(value: PointParseError) -> Self {
-        TreeParseError::Point(value)
+        Self::Point(value)
     }
 }
 
 impl<E: Display> Display for TreeParseError<E> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            TreeParseError::Boolean(boolean_error) => {
-                f.write_fmt(format_args!("failed to parse RB flag: {}", boolean_error))
+            Self::Boolean(boolean_error) => {
+                f.write_fmt(format_args!("failed to parse RB flag: {boolean_error}"))
             }
-            TreeParseError::Point(point_error) => f.write_fmt(format_args!(
-                "failed to parse RB tree reference: {}",
-                point_error
+            Self::Point(point_error) => f.write_fmt(format_args!(
+                "failed to parse RB tree reference: {point_error}"
             )),
-            TreeParseError::Key(key_error) => {
-                f.write_fmt(format_args!("failed to parse RB tree key: {}", key_error))
+            Self::Key(key_error) => {
+                f.write_fmt(format_args!("failed to parse RB tree key: {key_error}"))
             }
         }
     }