I..... don't think treating it like a chin up bar will work. You'll probably need some purchase to get the rest of your body up there, if it's just dangling dead weight. Try finding spots you can grab on the trunk and using them!

[Even if blunt human nails weren't inferior to claws for climbing, Shido had already kinda torn his nails and fingers up. This is really going to be a literally uphill battle, huh?]