There are a number of different ways to organize your class tree when using the URL category classification feature. The best class tree to use is one that fits your needs. Consider the following to determine what type of traffic tree to create:
Do you want to find out which categories users are accessing?
Are you interested in monitoring (and perhaps blocking) traffic from specific categories?
Do you want to treat secure and unsecure traffic for a specific category differently?
Are you more interested in monitoring types of categories, rather than specific categories?
Based on preliminary research, Blue Coat has come up with several recommended tree designs for URL categories. See the following link for details.