I doubt it would kill a tree, but please remove them when you are thru using the tree as a hunting blind support. Those things will be in there long after you are gone and if some innocent sawmill worker is in the wrong place when that tree is cut for lumber there is a possibility of severe injury or death to that worker. Band saws will basically explode when they hit a spike/bolt in a log. Most sawmills use metal detectors, but they are not 100%. Why not just get a good ladder stand. Lighter, can be moved easily, safer and probably cheaper than building a stand.