Calculate the differences between the given trees.

        :param dict pytree: The dictionary of the parsed Python tree.
        :param dict doctree: The dictionary of the parsed documentation tree.
        :rtype: tuple
        :returns: A two-tuple of sets, where the first is the missing Python files, and the second
            is the missing documentation files.

def calculate_tree_differences(self, pytree, doctree):
        """Calculate the differences between the given trees.

        :param dict pytree: The dictionary of the parsed Python tree.
        :param dict doctree: The dictionary of the parsed documentation tree.
        :rtype: tuple
        :returns: A two-tuple of sets, where the first is the missing Python files, and the second
            is the missing documentation files.
        """
        pykeys = set(pytree.keys())
        dockeys = set(doctree.keys())

        # Calculate the missing documentation files, if any.
        missing_doc_keys = pykeys - dockeys
        missing_docs = {pytree[pyfile] for pyfile in missing_doc_keys}

        # Calculate the missing Python files, if any.
        missing_py_keys = dockeys - pykeys
        missing_pys = {docfile for docfile in missing_py_keys}

        return missing_pys, missing_docs