Return tuples for all parent GO IDs, containing current GO ID and parent GO ID.

def get_all_parent_edges(self):
        """Return tuples for all parent GO IDs, containing current GO ID and parent GO ID."""
        all_parent_edges = set()
        for parent in self.parents:
            all_parent_edges.add((self.item_id, parent.item_id))
            all_parent_edges |= parent.get_all_parent_edges()
        return all_parent_edges