How to assign several Business Unit to employees so it can be shown on Opportunities (CX)?

I have created users and assigned them as employees but the system only allow you to assign a single BU to a user.
Our requirement is to filter the shown values on Business Unit field on Opportunity object by user.

The tool we can use is Resource Directory.
Is there a way to assign more than 1 BU to a resource member using HCM module (Resource Directory) so the BUs can be shown on available Business Unit on Opportunity creation page?