Make a multi-colored light-up tree topper with Arduino and WS2812 LEDs. The toppers are interchangeable, so make 1 core and then choose which topper you want this year.

Make your own topper by making a hollow design. Use the attached 123D Design files and add the inner ring for the core to slot into.
The attached Arduino code gives you 6 solid color selections and a twinkle effect that randomly changes the colors. Modify this to add your own effects. You'll need the Adafruit Neopixel library here: https://learn.adafruit.com/adafruit-neopixel-uberguide/arduino-library
I simply used hot glue to attach the lights, button, and Arduino to the center tube.