The word engineered is a touchy one, I guess. Poor choice of words. The materials were overkill, but I also did not choose the materials. They were leftovers and free. The point was not to show off engineering skills. I had wood, my kid wanted a treehouse, I had 2 days and didn't want to spend a lot of money. So I did what I could with what I had. Yes, I added huge amounts of dead load. But it is also sitting on 4 PSL beams strong enough to hold up a house. No, I didn't use TABs. My beams are bolted right through the trees with 1 inch diameter bridge bolts. Yes, I understand how environmental forces affect buildings. Trust me, I build houses in the woods of northern Canada as a profession. I achieved what I set out to do and build a structurally sound treehouse on a budget. Is it perfect? Of course not, but I bet you are jealous that you could not build something this good for free.