Maximum difference between node and its ancestor

Given a Binary Tree you need to find maximum value which you can get by subtracting value of node B from value of node A, where A and B are two nodes of the binary tree and A is an ancestor of B.

Latest Source Code:
Github: BinaryTreeMaxNodeDiff.java

Output:

        8               
      / \       
     /   \      
    /     \     
   /       \    
   3       10       
  / \       \   
 /   \       \  
 1   6       14   
    / \     /   
    4 7     13   
                                
Max diff: 7