Inspired by the Christmas tree by idig3d, but customizable. This way, we don't all have to print the same tree, which is especially nice if you want to put multiple next to each other. Open the scad file in OpenSCAD to customise the model.

Print in vase mode. Bottom layers aren't needed. Be careful with layer heights and the bottom sides of the lowest branches. If you choose your layer height too tall, the branches may suffer from too steep overhangs. I print with 0.15 mm layer height. These overhangs also depend on the way you customize the tree. Check in your slicer.

I also included some example STLs that you can output with the OpenSCAD file.