input:                         
  def dropLeafNodes(head): 
      """
      Implement a function in Python that takes a Huffman tree and removes all its leaf nodes.
      
      >>> dropLeafNodes(None) is None
      True
      >>> dropLeafNodes(Node(1)) is None
      True
      >>> dropLeafNodes(Node(1, Node(2), Node(3)))
      Node(1, Node(2), Node(3))
      >>> dropLeafNodes(Node(1, Node(2, Node(4), Node(5)), Node(3, Node(6), Node(7))))
      Node(1, Node(2), Node(3))
      """
      if head and not head.left and not head.right: 
          return None
      
      if not head: 
          return None
      
      head.left = dropLeafNodes(head.left) 
      head.right = dropLeafNodes(head.right) 
      
      return head
output:     if not head.left and not head.right:
          return None