I have never built a treestand from wood, but I have built a ton of treehouses is the same configurations. Nailing or bolting 2x4s to trees is difficult to do well. One thing I DID learn is that you NEVER cross over between two trunks. When the wind blows they move relative to each other and will pull out or break any wood between them.

It is much safer if you are going to do this if you build it all on one trunk. 2 2x4s for the base (in a triangular pattern, meeting 3 feet behind the tree), 2 more for the downward diagonals, three for the frame around the platform. It can be done safely if you understand that everything is moving in the woods and learn to design to accommodate that movement. Plus, never use nails. Treated decking screws and lag bolts and screws only.

Chubber