//all nodes to the right and above current can be added to the value of the current node
//***How can I think about this? I try thinking about it visually and it's very slow to draw out the call stack
//is there a more effective way ? Often I get lost in the call stack.

var sum = 0;
var convertBST = function(root) {

if(root === null) return null;
convertBST(root.right);
root.val += sum;
sum = root.val;
convertBST(root.left);
    console.log('x',root);
return root;
};