add prefix

app.py

@@ -137,15 +137,13 @@ def insert(self, val):
 """
 
 display_code = r"""
-def display_tree(self):
+def display_tree(self: Tree, prefix='value: '):
     current_node = self.val
     
     if self.left:
         self.left.display_tree()
     
-    print(
-        f'value: {current_node}'
-    )
+    print(prefix, current_node)
     
     if self.right:
         self.right.display_tree()