I basal tie most of my climbs, it seems to be a minority move, but that's another discussion.
I also like it when my line has more than one branch below it to catch if for some reason the top one failed.
When securing my line at the bottom of the tree, I tie an alpine butterfly, clip a steel carabiner into it, then capture the rope going up the tree in the biner. I am leery of rope on rope for base tie in SRT, sometimes when you are climbing, you unweight the system, depending on how much friction is present the whole thing can go slack and droop, right down to where you have it tied at the bottom. Re-weighting the system then tightens it up again, there is the potential for your bowline to be rubbing and chafing where it is tied around your line going up the tree.
A guy posted a picture on FB of wear in a rope only base tie...ok, he must have been heavy and moving around a lot but it proved the point that it can happen!