You retrieve a FS like this by connecting a little 'harp' (a little connecting divice that is one milimeter wider than the clinbing rope) to the climbing rope (the side that goes from the pulley to the friction hitch).
So, if you unclip from your saddle, the end of the rope goes up into the tree, thru the pulley, gets stuck in the 'harp', the harp puls on the end of the FS, the pulley is pulled out of the ring and the whole kit tumbles down.
If you are happy with the kit you use and if your life means something to you, than you put a throwline on the end of the climbingline before the rope is pulled out of the tree.
In the attachment is a new version I made /forum/images/graemlins/laugh.gif
This is how it´s made:
1. Take a normal version friction saver (mine is a Cresto 130cm long).
2. Cut the big ring out with a hacksaw.
3. Put in a ART pulley.
4. Take a new big friction saver ring and install this to a little sling (30cm long).
5. Put the sling on the friction saver via a prussic.
Done.
The fun part of this FS is that it can be installed in the tree in the way you are used to do with a normal double ring FS. Work in the tree upwards and if you think "hé I don't need to climb all the way up" than you retrieve it with a little ball (and of course a trowline) on the end of your climbing line.
BUT, if you go all the way up, than you tie in with the flipline next to the FS. De-attach the climbing line from the FS and attach it in the way that is shown in the picture.
Climb safe.