They do exactly what I need. Just a note: to use a butterfly anchor you will need to drill a hole with a 9/16 bit. The closest bit size I could find was 1/2, but I made it work by wiggling the bit around to widen the hole. They didn't come with instructions, so I'll add: the shorter the screw, the more it will stick to the tree, the longer the screw and butterfly anchor for attachment to the drywall.
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