How to set up hierarchy for Product categories in SRM

We are in Extended Classic scenarion in SRM 7.01.We have over 500 UNSPSC Codes as Product categories and it is difficult for users to search the ones they want.User experience will be better if we set up as Hierarchies while creating Shopping cart similar to MDM where all the Product categories are grouped under hierarchies.

We dont replicate any materials or create any material codes in SRM. SC is created as free text with or without reference to contract  or catalog (Internal or external) .

Product categories are replicated from ECC using T.code R3AS.

Any inputs will be appreciated.

Thanks

Balaji