Add all greater values to every node in a given BST

Given a Binary Search Tree (BST), modify it so that all greater values in the given BST are added to every node

class TreeNode(object):
    def __init__(self,val):
        self.value = val
        self.left  = None
        self.right = None

    def __repr__(self):
        return str(self.value)

class Solution(object):
    def add_larger_values(self,root):
        self.sum = 0
        self._add_larger_values(root)

    def _add_larger_values(self,root):
        if not root:
            return
        self._add_larger_values(root.right)
        temp = root.value
        root.value += self.sum
        self.sum +=temp
        self._add_larger_values(root.left)

Observation:

It is similar to inorder traversal, as in inorder traversal u call print statement only once , so is in this case added root value to sum should be done only once