Masterpage in ASP.NET

I have master page with 12 menus. I have three login namely

1. Admin
2. employee
3. customer

I want to show these menus according to these three login. how to separate these under coding? I want to show every menus for admin, If admin login
if employee login the page means need to show only employee details like that.now I have only one master page, which is common for all three. can u tell me...?