It’s probably too late for you to get a hotel at this point. They normally book out a year in advance. I would look at Cashmere or Wenatchee for lodgings.

Be prepared for a huge crowd and cold weather. Make sure your tires are in good condition and you have chains (and know how to use them). Check pass reports for Bluet and Snoqualmie pass. I would get there and park an hour before everything opens. Parking is extremely limited and you need to be there the entire day to enjoy the tree lighting.

Plan on visiting the sites in Cashmere and Wenatchee. There’s really only one days worth of activity in Leavenworth.