Y'know, the tree really doesn't look too bad. Take off the old sisal, give the carpet a good cleaning, and put on new sisal. Presto, chango, a "new" cat tree. And cheap too.
100 ft of sisal cost me less than 7 bucks at Home Depot a couple of weeks ago. Paddy looks so comfy in his house. I'd hate to take it from him and maybe get one he wouldn't like.