Is it possible to do a Dynamic category (say for new products) from a main category that includes all of its sub categories?

Thanks

well id like to do a dynamic category of new products in last 7 days.

catagories structure i have is say Hair (Main) Sub Categories of Scissors (L2), Shampoo (L2) & even a couple of Sub categories off of the L2.

Id like to do new products in lst 7 days of category Hair & include all of its sub categories.

hope this makes sense