The printable Christmas Tree by idig3d is a really cool model - I just didn't want it to sit flat on the table, so I printed it with a solid bottom and designed this little trunk base to put it on.

I tried to design it so that it roughly matches the style of the tree model.

Simply print it with brown filament and attach it to the tree with some glue double-sided tape.

Hint: If you print the tree with a "Concentric" line pattern for the first layer fill, you get a nice "crosshair" to get the trunk exactly centered. ;-)

(You can find the Power Star Topper from the photo here, by the way: https://www.thingiverse.com/thing:5661658)