diff --git a/doc/cheatsheet/bfs.md b/doc/cheatsheet/bfs.md
index 27fe218c..45175673 100644
--- a/doc/cheatsheet/bfs.md
+++ b/doc/cheatsheet/bfs.md
@@ -56,10 +56,14 @@ def bfs(root):
         return
     q =[]
     q.append(root)
-    while root:
+    while q:
         for i in range(len(q)):
-            ### NOTE : we need to pop the 1st element (idx = 0), BUT NOT THE LAST element
-            #        -> default is pop last element (e.g. q.pop() equals q.pop(-1))
+            """
+            ### NOTE : 
+
+                we need to pop the 1st element (idx = 0), BUT NOT THE LAST element
+                -> default is pop last element (e.g. q.pop() equals q.pop(-1))
+            """
             root = q.pop(0)
             # do sth
             if root.left:
diff --git a/doc/cheatsheet/dfs.md b/doc/cheatsheet/dfs.md
index 57103440..8b9e58ad 100644
--- a/doc/cheatsheet/dfs.md
+++ b/doc/cheatsheet/dfs.md
@@ -30,6 +30,39 @@
 
 ### 0-2) Pattern
 
+#### 0-2-1) General form
+
+```python
+# form I
+def dfs(root):
+
+    # if root, do sth
+    if root:
+        # do sth, pre-order (root->left->right) in this code
+
+    # if not root, do NOTHING
+
+    # if root.left exist
+    if root.left:
+        dfs(root.left)
+    # if root.right exist
+    if root.right:
+        dfs(root.right)
+
+# form II
+def dfs(root):
+
+    # if root, do sth
+    if root:
+        # do sth, pre-order (root->left->right) in this code
+
+    # if not root, nothing to do
+
+    dfs(root.left)
+    dfs(root.right)
+```
+
+#### 0-2-2) Basic Tricks
 
 - Important !!!!
 ```java
@@ -51,6 +84,8 @@ private TreeNode _dfs(TreeNode node){
 }
 ```
 
+- Tree transversal (DFS)
+
 ```python
 # python
 # form I : tree transversal
@@ -68,6 +103,8 @@ def dfs(root, target):
        # do sth
 ```
 
+- Tree value moddify (DFS)
+
 ```python
 # form II : modify values in tree
 
@@ -109,11 +146,14 @@ class Solution(object):
         """
         if not root: 
             return TreeNode(val)
+
         if root.val < val: 
-            root.right = self.insertIntoBST(root.right, val);
+            root.right = self.insertIntoBST(root.right, val)
+
         elif root.val > val: 
-            root.left = self.insertIntoBST(root.left, val);
-        return(root)
+            root.left = self.insertIntoBST(root.left, val)
+
+        return root
 ```
 
 ```python
@@ -168,38 +208,6 @@ test()
 print (z)
 ```
 
-## 1) General form
-```python
-# form I
-def dfs(root):
-
-    # if root, do sth
-    if root:
-        # do sth
-
-    # if not root, nothing to do
-
-    # if root.left exist
-    if root.left:
-        dfs(root.left)
-    # if root.right exist
-    if root.right:
-        dfs(root.right)
-
-# form II
-def dfs(root):
-
-    # if root, do sth
-    if root:
-        # do sth
-
-    # if not root, nothing to do
-
-    if root.left:
-    dfs(root.left)
-    dfs(root.right)
-```
-
 ### 1-1) Basic OP
 
 #### 1-1-1) Add 1 to all node.value in Binary tree?
diff --git a/leetcode_python/Tree/find-duplicate-subtrees.py b/leetcode_python/Tree/find-duplicate-subtrees.py
index 092292a3..6362f3c5 100644
--- a/leetcode_python/Tree/find-duplicate-subtrees.py
+++ b/leetcode_python/Tree/find-duplicate-subtrees.py
@@ -65,12 +65,27 @@
 #
 # In [36]: m
 # Out[36]: defaultdict(int, {0: 0, 1: 1, 2: 1})
+#
+# Example 1 : root = [2,1,1]
+# output :
+#      >>> m = defaultdict(<type 'int'>, {'2-1-#-#-1-#-#': 1, '1-#-#': 2})
+# 
+# Example 2 : root = [2,2,2,3,null,3,null]
+# output :
+#      >>> m = defaultdict(<type 'int'>, {'2-2-3-#-#-#-2-3-#-#-#': 1, '2-3-#-#-#': 2, '3-#-#': 2})
+#
+# Example 3 : root = [1,2,3,4,null,2,4,null,null,4]
+# output :
+#     >>> m = defaultdict(<type 'int'>, {'4-#-#': 3, '1-2-4-#-#-#-3-2-4-#-#-#-4-#-#': 1, '2-4-#-#-#': 2, '3-2-4-#-#-#-4-#-#': 1})
+#
+#
 import collections
 class Solution(object):
     def findDuplicateSubtrees(self, root):
         res = []
         m = collections.defaultdict(int)
         self.dfs(root, m, res)
+        #print(">>> m = " + str(m))
         return res
 
     def dfs(self, root, m, res):