Have had the same treestand backpack for over 20 years and it is time to consider a new one.
Not sure if you're talking about a backpack made to pack in your treestand,
or a backpack to hang on your treestand (or tree) once you're there?
I've experimented with a variety of backpacks & pack frames for the purpose of carrying in & out a treestand & gear. None of these have been "good", as they add so much weight (and time to the process) that I'd rather just use backpack straps on a tree stand, and strap my gear to the stand (with the stand serving as a "back pack").
When doing this, I use a fanny pack, which is strapped to my tree stand, in & out. The fanny pack is much easier to work with up in a tree than a larger backpack. And, should I leave the stand overnight, have the fanny pack for bringing out my gear.
Fairchaser's vest idea works fine as well, but I normally have some long walks, and wear as little as possible walking in, so as not to sweat as much. I normally want nothing beyond a shirt for walking in, with all my outer clothing either packed in or on the fanny pack, plus heavier clothing is simply strapped to my stand being used as a backpack.
If I leave the stand overnight, my fanny pack is large enough I can strap a heavy parka on it for walking out & back in. Large fanny pack works for me better than a vest or larger backpack. I don't sweat as much walking with a fanny pack as a vest or backpack. You also will not seat as much from using a treestand as a pack frame (compared to most backpacks).