Hide Subtotal Row If Only One "Item" In Group

[mikeys]

Hi,

How can I hide a child row where there is only one item in the group?
I have 3 groups:
Parent = Brand,
 Child = Model,
  Child = Year.

I want to hide the Model child group if it has only 1 value, since the parent is displaying the same information.
I have tried many variants but can't get it.