Search Multicategory

I search for a solution for:
search sub category in two different main categorys.
eg.
Category 1
SubCategory 1
SubCategory 2
Category 2
SubCategory 1
SubCategory 2

There should be possibility to for eg. show all post from Cat 1 / SubCategory 1 and Cat 2 / SubCategory

Is there anybody that know how to do this, or if there is any plugin for it, have search but dident found anything

Thanks