diff --git a/CS notes/pages/Leetcode Maximum-Depth-Of-Binary-Tree.md b/CS notes/pages/Leetcode Maximum-Depth-Of-Binary-Tree.md
index b6b0c3b..9b56d80 100644
--- a/CS notes/pages/Leetcode Maximum-Depth-Of-Binary-Tree.md	
+++ b/CS notes/pages/Leetcode Maximum-Depth-Of-Binary-Tree.md	
@@ -56,12 +56,38 @@ BFS way:
 Simply log the level in each while iteration.
 
 DFS way: (Popular)
-Use recursion
+Use recursion:
+- Base Case:
+	- root == nullptr: return 0;
+- maxDepth(root) = max(maxDepth(root->left), maxDepth(root->right))
 
 ### Solution
 
 DFS Recursion:
 ```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
+ * right(right) {}
+ * };
+ */
+class Solution {
+public:
+  int maxDepth(TreeNode *root) {
+    // DFS
+    if (!root) {
+      return 0;
+    }
+
+    return max(maxDepth(root->left), maxDepth(root->right)) + 1;
+  }
+};
 ```
 
 BFS: