BST and Binary Tree Assignment:replace with Sum of greater nodes

public class Solution {

/*	Binary Tree Node class
 * 
 * class BinaryTreeNode<T> {
		T data;
		BinaryTreeNode<T> left;
		BinaryTreeNode<T> right;
		
		public BinaryTreeNode(T data) {
			this.data = data;
		}
	}
	*/
	
	public static void replaceWithLargerNodesSum(BinaryTreeNode<Integer> root) {
		if(root == null){
            return;
        }
        int ans = replace(root ,0);
        
		
	}
    public static int replace(BinaryTreeNode<Integer> root ,int sum){
        if(root == null){
            return 0;
        }
        
        int right = replace(root.right ,sum);
        int rootdata = root.data;
        root.data = root.data + right + sum;
        int left = replace(root.left ,root.data);
        
        return rootdata + right + left;
        
    }
}