asp.net webforms routing: optional parameters

I want to add optional parameters in my routing table. For example I would like the users to browse a product catalog like this: http://www.domain.com/browse/by-category/electronics/1,2,3 etc

Now i've created a route like this:

            routes.MapPageRoute(
           "ProductsBrowse",
            "browse/{BrowseBy}/{Category}",
            "~/Pages/Products/Browse.aspx"
        );

Problem however is that when a user enters http://www.domain.com/browse , I would like them to present a different page where they can pick the manner on how to browse. So the parameters {BrowseBy} and {Category} will not be used.

Is there a way around this then to create seperate routes for each of the scenarios?

Thank you for your time! Kind regards, Mark