input: Write a function that takes a Huffman tree and drops all its leaf nodes. The function should return the modified tree with all leaf nodes removed. The leaf nodes are those with no children.
  
  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,), (5,)), (3, (6,), (7,))))==((2, (4,), (5,)), (3, (6,), (7,)))
  assert dropLeafNodes((1, None, None))==None
  assert dropLeafNodes((1, (2, (3, None, None), None), None))==((2, (3, None, None), None),)
  assert dropLeafNodes(None)==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