Reimplements the :meth:`QAbstractItemModel.mimeData` method.

        :param indexes: Indexes.
        :type indexes: QModelIndexList
        :return: MimeData.
        :rtype: QMimeData

def mimeData(self, indexes):
        """
        Reimplements the :meth:`QAbstractItemModel.mimeData` method.

        :param indexes: Indexes.
        :type indexes: QModelIndexList
        :return: MimeData.
        :rtype: QMimeData
        """

        byte_stream = pickle.dumps([self.get_node(index) for index in indexes], pickle.HIGHEST_PROTOCOL)
        mime_data = QMimeData()
        mime_data.setData("application/x-umbragraphmodeldatalist", byte_stream)
        return mime_data