getResources - how show all resources in parent

Example:

Product A (1)
- product A.A (2)
- product A.B (3)
- product A.C (4)
Product B (5)
- product B.A (6)
- product B.B (7)
- product B.C (8)

How show all products A and separately B but &parents=`??` is parent of this products A.B.
One solution is &parents=`1` but I need automatically insert parents number of product A.B.

Is any solution like &parents=`one level up`

I hope that is understandable. Simply I need parents number based on resource.

Best regards

Try

@ottogal

Thank you very much, works great.