diff --git a/basic_data_structure/__init__.py b/basic_data_structure/__init__.py
index 21290f6..117eb6c 100644
--- a/basic_data_structure/__init__.py
+++ b/basic_data_structure/__init__.py
@@ -73,6 +73,7 @@ def main():
     node = lst[4]  # get node
 
     print('Saved node:', node.value)
+    # Output: Saved node: 3
 
     lst.insert(4, 4)  # insert new value into list
     lst.append(2)  # append a new value
@@ -83,17 +84,18 @@ def main():
     lst.reverse()  # reverse list
 
     print('List length:', len(lst))  # length of the list
+    # Output: List length: 9
 
+    # iteration over values
     for val in lst.values():
-        # iteration over values
         print(val, end=' ')
 
     # Output: 1 2 3 4 5 6 7 8 9
 
     print('')
 
+    # iteration over nodes
     for node in lst:
-        # iteration over nodes
         print(node.value, end=' ')
 
     # Output: 1 2 3 4 5 6 7 8 9
@@ -157,13 +159,9 @@ def generate_tree() -> TreeNode:
 def dfs(root: Optional[TreeNode]) -> Generator[int, None, None]:
     \"""Depth-first search.\"""
     if root:
-        if root.left:
-            yield from dfs(root.left)
-
+        yield from dfs(root.left)
         yield root.value
-
-        if root.right:
-            yield from dfs(root.right)
+        yield from dfs(root.right)
 
 
 def main():
diff --git a/basic_data_structure/linked_list.py b/basic_data_structure/linked_list.py
index c34e16f..a339f97 100644
--- a/basic_data_structure/linked_list.py
+++ b/basic_data_structure/linked_list.py
@@ -17,6 +17,7 @@ def main():
     node = lst[4]  # get node
 
     print('Saved node:', node.value)
+    # Output: Saved node: 3
 
     lst.insert(4, 4)  # insert new value into list
     lst.append(2)  # append a new value
@@ -27,17 +28,18 @@ def main():
     lst.reverse()  # reverse list
 
     print('List length:', len(lst))  # length of the list
+    # Output: List length: 9
 
+    # iteration over values
     for val in lst.values():
-        # iteration over values
         print(val, end=' ')
 
     # Output: 1 2 3 4 5 6 7 8 9
 
     print('')
 
+    # iteration over nodes
     for node in lst:
-        # iteration over nodes
         print(node.value, end=' ')
 
     # Output: 1 2 3 4 5 6 7 8 9
diff --git a/basic_data_structure/nodes/tree_node.py b/basic_data_structure/nodes/tree_node.py
index 79431a9..8d124b4 100644
--- a/basic_data_structure/nodes/tree_node.py
+++ b/basic_data_structure/nodes/tree_node.py
@@ -65,13 +65,9 @@ def generate_tree() -> TreeNode:
 def dfs(root: Optional[TreeNode]) -> Generator[int, None, None]:
     \"""Depth-first search.\"""
     if root:
-        if root.left:
-            yield from dfs(root.left)
-
+        yield from dfs(root.left)
         yield root.value
-
-        if root.right:
-            yield from dfs(root.right)
+        yield from dfs(root.right)
 
 
 def main():