You're right of course, it is a fig-8 in a bight!
The difference between this and a rock climb is that I was using adjustable lanyards while climbing (slings have no stretch and can't be adjusted to eliminate slack), and not climbing above them (because the shock load of taking a fall onto your lanyard could easily snap a branch). Also the rope was static - fixed at the top, instead of running through the carabiner with a be_layer_ taking in the rope, which would happen in rock climbing.
If you do try this then make sure your route to the top is as straight as possible. If not then should a person decide to hang on the rope then it could bend and flick past a branch and she will go for a swing
For the attachment point, double wrap the sling around the trunk or go a girth hitch so that the sling grips the trunk rather than loading the thin conifer branches.
To remove the rope I untied the knot and put the rope back into the carabiner. then I got Jackie to slowly pull the rope through from the abseil end. When the end passed through the biner it fell straight to the ground under its own weight because the abseil route was completely vertical - no tangles!
There are only 3 conifers in the vicinity, the rest are shorter beeches and larches so there is a clear view across the treetops with a few other tall conifers as distant landmarks (I've been up most of those too!)
