I've tried to stay away from endorsing products or from selling anything to keep my motives more pure, but a couple folks asked so I figured I'd put this up. It's what I think the best way to have Thomas around your Christmas Tree. As I'm a bit of a Percy nut, I firmly believe that no winter Thomas train would be complete without Jack Frost Percy. Note that Jack Frost Percy isn't motorized, so you would either need to use him with the motorized Thomas from the Wooden Holiday railway set, or use the motorized Percy below (though having a motorized Percy pull a different Percy strikes as too out-there -- though I'm on-board with talking trains... what gives?
Alternatively, this set is larger (but I find the plastic trains kind of junky... I'm a sucker for wooden toys). If the plastic doesn't bother you, this one might make a better Holiday Tree loop because it won't look so scrawny under the tree. Note though that this train typically uses the plastic blue track, which isn't included in this set. The train works on the standard wooden track if you put it together properly (don't have any joints that are stressed) but I think it looks a little funny... top heavy like a 2 liter bottle standing upside down. Again, that's just my preference.
Big Blue Train Set