input: Write a function to implement a function in Python that takes a Huffman tree and drop all its leaf nodes. If a node is a leaf, return None; otherwise, recursively process the left and right subtrees and 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((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`
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