Restrict user to access and view only own BU data

Hi,

I have created different business units, add user in business unit and assigned role like salesperson, sale manager, VP sales.

I want to restric visibility of all record at business unit level. for example BU-A user can only see leads and opportunity to their own BU and now allow them to see other business unit like BU-B details.

pls guide how to implement these restrictions.

Thanks.