title: Find the node with given value in binary tree in in-order way and return it
body: <p>find the node in binary tree in inorder way, and return it
  PS： the binary tree may include two nodes with the same value.
  it's easy to do it in pre-order way</p>
  
  <pre><code>Node find(Node root, int val){...}
  </code></pre>
  
  <p>anyone can share a solution?</p>