B tree find nodes greater than key

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Python

I have a b tree and I am given a key and I need to return the number of nodes that are greater than the key. I tried many ways but I can't get this problem I think the confusing part is how to go back to check the next children. So far I just implemented the search but not sure how to go back up to the root.

What I have tried:

def _nums_larger(self, k, node):
      if node is None:
        return 0
      count = 0
      for key in node.keys:
        if key > k:
          count +=  1
      if node.is_leaf:
        return -1
      for i, key in enumerate(node.keys):
        if key > k:
          count += self._nums_larger(k,node.children[i])
      self._nums_larger(k, node.children[-1])
      return count