class Solution {
    public int maxProduct(TreeNode root) {
        if(root == null){
            return 0;
        }
        return Math.max(sum(root.left, root.val), sum(root.right, root.val));
    }

    public int sum(TreeNode root, int sumAbove) {
        if(root == null) {
            return 0;
        }
        int left = sum(root.left, root.val);
        int right = sum(root.right, root.val);
        int max = Math.max((left+sumAbove) * (right), (right+sumAbove) * (left));
        max = Math.max(max, root.val);
        return max;
    }
}