You have to make different fields for different levels so that you could use them as dimensions.
Lets assume you have three fields:
AllProducts - this one have the only one value for all products.
Category - this is for product categorys
Products - this is the name of the particular product.
Then you can create a drill-down or cyclic group from that dimensions (Document properties->Groups tab).
Now you could use this group as dimension.
Note that 'All products' field will be omitted for drill-down group as QV jumps to the next level when there is only one value on the current.