Add an insert document to the list of ops.

def add_insert(self, document):
        """Add an insert document to the list of ops.
        """
        validate_is_document_type("document", document)
        # Generate ObjectId client side.
        if not (isinstance(document, RawBSONDocument) or '_id' in document):
            document['_id'] = ObjectId()
        self.ops.append((_INSERT, document))