The talented ladies at my local public library created a few charming book trees out of a seldom-used set of reference books, a string of lights, and an old, unreadable book. Perhaps you have similar supplies around the house?
Your collection of Babysitters' Club book would make a perky, pastel tree, while the complete works of James Patterson would create a huge and darkly dramatic tree, full of ominous titles such as 1st To Die and Cross Fire. Bonus points for Merry Christmas, Alex Cross! A set of leatherbound books with gold writing would make for a particularly rich and glamorous tree.
Simply arrange a layer of books in a rough circle, and build from there, staggering the books across the gaps in each previous layer, and moving inward as you work. It may take a few attempts (or a particularly analytical mind) to figure out how big to make each layer, but it's a mess-free low-stress sort of problem to figure out. Once the books are stacked to your liking, drape sparkly lights around the whole thing.
If you'd like to take the theme even further, use an unwanted book to create a book tree topper- a tutorial can be found at Creative "Try"als. You could also use any paper that matches your color scheme to craft a folded paper tree to put on top - Julep and Madame Bonbon have tutorials.
If you do create a book tree, please show off a photo!