While we've had the traditional live tree, we've explored other options these past few years, such as our 2011 tree. It was at the start of a project to catalog our books and was made entirely of books from authors we personally knew at the time, or of BookCrossing books that needed to be released. The true family collection, which turned out to be around 7,000 books, remained untouched. Just heard back from one of the novels, which was released via BookCrossing in 2012. It's now in Austria.
In 2012, I chalked a Christmas tree on a piece of wood I'd painted with blackboard paint. 2013, I painted over the chalk with white acrylic and it did double duty for a second year.
Now we're in a new place-- the challenge is on.