Insert a Version child PID.

def insert_child(self, child_pid, index=-1):
        """Insert a Version child PID."""
        if child_pid.status != PIDStatus.REGISTERED:
            raise PIDRelationConsistencyError(
                "Version PIDs should have status 'REGISTERED'. Use "
                "insert_draft_child to insert 'RESERVED' draft PID.")
        with db.session.begin_nested():
            # if there is a draft and "child" is inserted as the last version,
            # it should be inserted before the draft.
            draft = self.draft_child
            if draft and index == -1:
                index = self.index(draft)
            super(PIDNodeVersioning, self).insert_child(child_pid, index=index)
            self.update_redirect()