Unfortunately I can't report on the diving (either sort), since I didn't do any. This was the first time either I or my buddy had snorkled; neither of us are SCUBA certified. We practiced from our pier before taking a tour, and were glad we did; I think it was much easier to acclimate to snorkling on our own time than during our first 15 minutes or so at Hol Chan.
As to the tree, I can't add much. My buddy and I wandered around south of town for a while (past the sign that reads: "<==Beach / Dump==>" ) and stopped at a likely-looking spot of beach to take some pictures. While creeping up on an egret to take a picture, my buddy stopped under a palm tree and...awakened something in the tree. I grieve that I didn't have a camera at the time.
We didn't do any more exploring that day. His spirits were somewhat dampened, and I had difficulty catching my breath for some little while afterwards.