Add a full remote desktop to a RemoteApp Session Collection

Go to...
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Terminal Server\CentralPublishedResources\PublishedFarms\<collection>\RemoteDesktops\<collection>

To show the Desktop Session Icon, Change the value (ShowInPortal) to 1 from 0.

You can also rename the Desktop Session Icon name to something more to your liking. To do this, change the value (Name).