Cross Reference Categories

I want to set up two main categories, and in those two main categories will be a bunch of sub-categories, but I want some of them to be the same because I will be adding all my products and then assigning them to those categories but I want to avoid assigning them to "Sub Cat A" and Sub Cat D" twice. Can that be done?

Ex.
Main:
Cat A:
Sub Cat A
Sub Cat B
Sub Cat C
Sub Cat D
Cat B:
Sub Cat A
Sub Cat D