Hi Vani,
Im dont worked with CRM, but maybe could you try to restrict it in a Customization (SPRO):
Customer Relationship Management/CRM Cross-Application Components/Multilevel Categorization
Maybe you can check the authorization object: CRM_CATEGO too.
But im not sure, maybe you can try to check it to ensure that is/not is your solution.
If not, I hope that any CRM consultant can help us with your requisition.
Please let us know with anything.
Best regards.