diff --git a/sorts/tree_sort.py b/sorts/tree_sort.py
index 78c3e893e..e63a3253b 100644
--- a/sorts/tree_sort.py
+++ b/sorts/tree_sort.py
@@ -1,53 +1,70 @@
 """
 Tree_sort algorithm.
 
-Build a BST and in order traverse.
+Build a Binary Search Tree and then iterate thru it to get a sorted list.
 """
+from __future__ import annotations
+
+from collections.abc import Iterator
+from dataclasses import dataclass
 
 
+@dataclass
 class Node:
-    # BST data structure
-    def __init__(self, val):
-        self.val = val
-        self.left = None
-        self.right = None
+    val: int
+    left: Node | None = None
+    right: Node | None = None
 
-    def insert(self, val):
-        if self.val:
-            if val < self.val:
-                if self.left is None:
-                    self.left = Node(val)
-                else:
-                    self.left.insert(val)
-            elif val > self.val:
-                if self.right is None:
-                    self.right = Node(val)
-                else:
-                    self.right.insert(val)
-        else:
-            self.val = val
+    def __iter__(self) -> Iterator[int]:
+        if self.left:
+            yield from self.left
+        yield self.val
+        if self.right:
+            yield from self.right
+
+    def __len__(self) -> int:
+        return sum(1 for _ in self)
+
+    def insert(self, val: int) -> None:
+        if val < self.val:
+            if self.left is None:
+                self.left = Node(val)
+            else:
+                self.left.insert(val)
+        elif val > self.val:
+            if self.right is None:
+                self.right = Node(val)
+            else:
+                self.right.insert(val)
 
 
-def inorder(root, res):
-    # Recursive traversal
-    if root:
-        inorder(root.left, res)
-        res.append(root.val)
-        inorder(root.right, res)
-
-
-def tree_sort(arr):
-    # Build BST
+def tree_sort(arr: list[int]) -> tuple[int, ...]:
+    """
+    >>> tree_sort([])
+    ()
+    >>> tree_sort((1,))
+    (1,)
+    >>> tree_sort((1, 2))
+    (1, 2)
+    >>> tree_sort([5, 2, 7])
+    (2, 5, 7)
+    >>> tree_sort((5, -4, 9, 2, 7))
+    (-4, 2, 5, 7, 9)
+    >>> tree_sort([5, 6, 1, -1, 4, 37, 2, 7])
+    (-1, 1, 2, 4, 5, 6, 7, 37)
+    >>> tree_sort(range(10, -10, -1)) == tuple(sorted(range(10, -10, -1)))
+    True
+    """
     if len(arr) == 0:
-        return arr
+        return tuple(arr)
     root = Node(arr[0])
-    for i in range(1, len(arr)):
-        root.insert(arr[i])
-    # Traverse BST in order.
-    res = []
-    inorder(root, res)
-    return res
+    for item in arr[1:]:
+        root.insert(item)
+    return tuple(root)
 
 
 if __name__ == "__main__":
-    print(tree_sort([10, 1, 3, 2, 9, 14, 13]))
+    import doctest
+
+    doctest.testmod()
+    print(f"{tree_sort([5, 6, 1, -1, 4, 37, -3, 7]) = }")