diff --git a/trees/bt_construct_inorder_postorder.py b/trees/bt_construct_inorder_postorder.py
index 697186d..59031b3 100644
--- a/trees/bt_construct_inorder_postorder.py
+++ b/trees/bt_construct_inorder_postorder.py
@@ -3,7 +3,7 @@
 # author: bt3gl
 
 
-def build_tree(left, right, index_map):
+def build_tree(left, right, index_map, postorder):
             
         if left > right:
                 return None
@@ -11,15 +11,15 @@ def build_tree(left, right, index_map):
         root = Node(postorder.pop())  # this order change from preorder
         index_here = index_map[root.val]
 
-        root.right = build_tree(index_here + 1, right, index_map) # this order change from preorder
-        root.left = build_tree(left, index_here - 1, index_map)
+        root.right = build_tree(index_here + 1, right, index_map, postorder) # this order change from preorder
+        root.left = build_tree(left, index_here - 1, index_map, postorder)
             
         return root
 
 
-def build_tree(inorder, postorder) -> Optional[Node]:
+def build_tree(inorder, postorder):
 
         index_map = {val: i for i, value in enumerate(inorder)}
             
-        return fill_tree(0, len(inorder) - 1, index_map)
+        return fill_tree(0, len(inorder) - 1, index_map, postorder)