input: Write a function to remove all leaf nodes from a given Huffman tree. The function should return the modified tree with all leaf nodes removed.
  
  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(Node(1, Node(2, Node(4), Node(5)), Node(3, Node(6), Node(7)))).left.left == None
  assert dropLeafNodes(Node(1, Node(2, None, None), Node(3, None, None))).left == None
  assert dropLeafNodes(Node(1, None, None)) == None
  assert dropLeafNodes(Node(1, Node(2, Node(4, None, None), Node(5, None, None)), Node(3, Node(6, None, None), Node(7, None, None)))).left.left == 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