More feature questions.

I wonder if you can add a sub folder to a root folder where the subfolder isn't an actual subfolder in the physical path of the root folder.

Also, can I tell each root folder whether or not to be expanded or not?

Thank you.

One more thing I noticed. It seems that the session expiration on this control can create error. Is there a way to adjust the session limit to match my application's session limit?

No, a root folder is just a pointer to a physical path but the subfolders are not pointers, they represent the actual physical structure under the root folder. So if you need to point to a different physical path or if you need to have a different permission set, you should create a separate root folder. 

The control uses ASP.NET's default Session module so session timeout should already match your application's. However if your application uses another mechanism to keep track of the sessions, then you can change ASP.NET's session timeout value (in minutes) in web.config to match your application's:

<sessionState mode="InProc"  timeout="20" />