code: def next(self):
      node = self.stack.pop()
      tmp = node
      if tmp.right:
          tmp = tmp.right
          while tmp:
              self.stack.append(tmp)
              tmp = tmp.left
      return node.val
  
label_desc: Use image node_id 3 for calling the BSTIterator obj's underlying member method code with example usage: obj.next() and returns: node