I’ve made a few, easy to do. 2x6 pressure treated wood, cut one piece longer than the other, like 6’ and 4’. Bolt together on one end to make like a scissor, make two of these. You lag bolt the shorter end to the tree, the longer side hangs down at about a 45 degree angle and lag bolt that. I pre drill w a cordless drill so screwing in the lag bolts is easier, I’m usulally hanging on w one arm, lol. You at that point can just screw pressure treated 2x4 pieces across your boards to make a platform, you can make a seat by leaving out a few boards or make some kind of seat. It’s pretty easy and cheap, I use at least 9/16’’ bolts or 5/8”.