This truly a multi-material project. There are two pieces that are 3D printed: the star topper that also doubles as our Circuit Playground Bluefruit case, and some mounts that hold our baubles in place in the drilled holes and allow us to mount the NeoPixels.
The star topper is actually a remix of the Circuit Playground case by the Ruiz brothers. I simply took the circular case and added the star points and a mount at the bottom. I also added cutouts in the back to access the pins on the Circuit Playground for soldering. You can download this remix on Thingiverse.
The mount is designed to serve two purposes: to hold the bauble in the hole and hold the NeoPixel button PCB. Both of these are done by force fitting in place. The mount actually fits inside the bauble's hole to press against the back of the tree to kind of sandwich the bauble in place. The NeoPixel button is then suspended snugly inside the mount so that it's centered nicely in the bauble. The Fusion360 file is available for the mount so that you can edit it to fit with your bauble or other mounting option. The .STL can also be downloaded on Thingiverse.