One-to-many relationship - way to quickly seed

Title probably makes no sense - sorry. But I'm trying to create a database for buildings with units. Eight buildings each with eight units. So I made a buildings collection that looks like this screenshot.

Then I made a collection called units. It has a attribute called unit_letter which is an enum that can be A,B,C,D,E,F,G, or H. The only other attribute is type "relationship". Not sure if it should be a one-way or two-way relationship. Both seem to work?

In any case is there a way to quickly fill in the units collection? In normal SQL it would be something like this:

INSERT INTO condos (building_id, unit_label) VALUES
(1, 'A'), (1, 'B'), (1, 'C'), (1, 'D'), (1, 'E'), (1, 'F'), (1, 'G'), (1, 'H'),
(2, 'A'), (2, 'B'), (2, 'C'), (2, 'D'), (2, 'E'), (2, 'F'), (2, 'G'), (2, 'H');
...