input: from typing import Optional
  
  class TreeNode:
      def __init__(self, value):
          self.value = value
          self.left = None
          self.right = None
  
  def dropLeafNodes(head: Optional[TreeNode]) -> Optional[TreeNode]:
      """ This function takes a Huffman tree represented by the head node and recursively
      drops all its leaf nodes. The tree is assumed to be binary.
      >>> root = TreeNode(1)
      >>> root.left = TreeNode(2)
      >>> root.right = TreeNode(3)
      >>> root.left.left = TreeNode(4)
      >>> root.left.right = TreeNode(5)
      >>> root.right.left = TreeNode(6)
      >>> root.right.right = TreeNode(7)
      >>> result = dropLeafNodes(root)
      >>> print(result.left is None and result.right is None)
      True
      """
      # 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
output:     # 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