def METHOD_NAME(self):
    super().METHOD_NAME()
    # check if operation type is in valid subtree
    if self._operation_type_subtree and self.type_id:
        type_root = OperationType.objects.get(
            pk=self._operation_type_subtree
        )
        if not self.type.is_descendant_of(type_root, include_self=True):
            raise ValidationError(
                'Invalid Operation type. Choose descendant of {}'.format(
                    self._operation_type_subtree
                )
            )