@knbk's answer didn't work for my use-case. The overridden method was not called.

I had to use a QuerySet and its as_manager method:

class SomeModelQueryset(models.QuerySet):
    def bulk_create(self, objs, *args, **kwargs):
        ...  # do something here

        super().bulk_create(objs, *args, **kwargs)


class SomeModel(models.Model):
    objects = SomeModelQueryset.as_manager()