Save this tree into a dumb data object for serialisation.

        The object must have attributes tree_size:int and hashes:list.

def save(self, other: merkle_tree.MerkleTree):
        """Save this tree into a dumb data object for serialisation.

        The object must have attributes tree_size:int and hashes:list.
        """
        other.__tree_size = self.__tree_size
        other.__hashes = self.__hashes