diff --git a/trees/bt_find_max_depth.py b/trees/bt_find_max_depth.py
index 8497a72..dbe2109 100644
--- a/trees/bt_find_max_depth.py
+++ b/trees/bt_find_max_depth.py
@@ -2,7 +2,8 @@
 # -*- coding: utf-8 -*-
 # author: bt3gl
 
-def max_depth(root: Optional[Node]) -> int:
+
+def max_depth(root) -> int:
         
         if root is None:
             return 0