input: Write a function that takes a Huffman tree and removes all its leaf nodes. The function should return the modified tree.
  
  def dropLeafNodes(head): 
      # If node is not None and doesn't have any children 
      if head and not head.left and not head.right: 
          return None
      
      # Don't change anything if head is None 
      if not head: 
          return None
      
      # Recursively call dropLeafNodes on left and right subtrees
      head.left = dropLeafNodes(head.left) 
      head.right = dropLeafNodes(head.right) 
      
      # Return head of the modified tree
      return head
  
  assert dropLeafNodes(None) == None
  assert dropLeafNodes((1, ((2, ((4, None), (5, None))), (3, ((6, None), (7, None)))))) == (1, (2, (None, ()) (3, (None, ()))))
output: def dropLeafNodes(head): 
      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