input: Write a function to drop all leaf nodes from a given Huffman tree. The function should recursively remove all nodes that do not have any children. If the tree is empty, return None.
  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(
        (1, (2, (4, None, None), (5, None, None)), (3, (6, None, None), (7, None, None)))
  )==(1, (2, None, None), (3, None, None))
  assert dropLeafNodes(
        (1, None, None)
  )==None
  assert dropLeafNodes(None)==None
output: def dropLeafNodes(head): 
      
      # If node is not None and doesn't have any children 
      if head and not head[1] and not head[2]: 
          return None
    
      # Don't change anything if head is None 
      if not head: 
          return None
    
      # Recursively call dropLeafNodes on left and right subtrees
      head = (head[0], dropLeafNodes(head[1]), dropLeafNodes(head[2]))
    
      # Return head of the modified tree
      return head