The tree models will need support.
To print this without lights, print tree-cutout.stl, and you don't need to print base.stl or tree-flat-bottom.stl. The star will need to be glued on top.
To print with lights, print tree-flat-bottom.stl, and base.stl, tree-cutout.stl isn't needed.
Print the tree with 0% infill.
Cura needed to print the bottom layers or the upper tiers wouldn't attach.
I had to take a razor blade and carefully cut off the bottom few layers to get access to the inside of the tree.
The grey/blue blobs on the inside is JB plastic weld, I broke off a few tiers when removing support.
For the lights, I used 2 LEDs and a 100 ohm resistor in series and put about 5 sets of those in parallel connected to a USB cable. It pulls around 30mA for me, so well below usb's power limits.
To light up the star I heated up a 3/16" drill bit with a lighter and drilled in the very top to allow a led to poke and shine through to the star. The star will need to be glued on top.(Hot glue/welders/goop will allow the led to shine through still)
Once the LEDs are in the tree and the top is lit, the tree just rests on the stand/base.
I used a little more JB plastic weld to hold it together.