You heat the pvc with a torch
You use nylon rope
You take a glob of silicone(preferably brown or black and put it in your hand and lather the rope up real well and stick it in a bucket with some peat already on the bottom of the bucket and then put more peat on top and try to compact it a bit pressing the peat onto the silicone firmly.
Make sure you score the pvc real well to allow the GS to stick to it and spray a bit on it to fill in the gaps and give it a rough look the carve it some and get rid of the smoothness of the GS....put your ropes on and silicone them in place or gorilla glue them in place would be better and then coat the tree part with silicone then press peat moss onto the silicone.
Do this in small areas don't try to do the whole thing at once....
This is how I would do it or just make it out of foam and not use pvc....