input: 
  def dropLeafNodes(head):
      """Remove all leaf nodes from a given Huffman tree. 
      >>> dropLeafNodes(head={(1): {(2): {(4): None, (5): None}, (3): {(6): None, (7): None}}})
      {(1): {(2): None, (3): None}}
      """
      
      # 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 head is a dictionary, convert it to a tree-like structure
      if isinstance(head, dict):
          head = {key: dropLeafNodes(value) for key, value in head.items()}
          # Remove keys with None values
          head = {key: value for key, value in head.items() if value is not None}
          # If all children are removed, return None
          if len(head) == 0:
              return None
          return head
  