Product Category Hierarchy

Hi experts!

I want to activate the product category hierarchy which I already activated in SRM customizing. I plan the following product category hierarchy:

Top-Level: IT

Sub-Levels: IT Maintenance; IT Software & Licenses; IT Equipment

We replicate the materialgroups from backend R/3.

Do I have to create all levels in R/3 and replicate them to SRM or can I somehow create the top-level locally in SRM and assign the sub-levels replicated from R/3.

Any documentation on this would be helpful.

Many thanks for your help which is very much appreciated.

Best regards,

Corinne