Remove sap or pine pitch stuck to their fur with vegetable oil. It does seem to be a good place to sleep as well. Most reports will give them 2-3 feet max. Some will not climb, but stretch and get whatever they can from the ground. Avoid any breakable ornaments on the bottom 2-3 feet.
Smaller objects have a tendency to end up under the couch.
I guess there's so much to do with that tree that chewing is not fun enough. Using a ground fault plug may still be a good idea. More fun when they are on or blinking. I would avoid tinsel. Some people suggested an alternative, but I'll let you use your imagination.