Bulk insert documents.

def bulk_insert(self, resource, docs, **kwargs):
        """Bulk insert documents."""
        kwargs.update(self._es_args(resource))
        parent_type = self._get_parent_type(resource)
        if parent_type:
            for doc in docs:
                if doc.get(parent_type.get('field')):
                    doc['_parent'] = doc.get(parent_type.get('field'))

        res = bulk(self.elastic(resource), docs, stats_only=False, **kwargs)
        self._refresh_resource_index(resource)
        return res