In order to be able to select (and summarize) at both levels, you need to load your data using the keywords HIERARCHY and HIERARCHYBELONGSTO. Look up these terms in the manual. They create an unbalanced hierarchy that allows the kind of functionality that you are trying to implement.
you have to add seperate field values to your new field "PROD_vs_RODZ_PROD" containing only the PRODUKT values to be able to select the PRODUKT groups.
hope this helps