The tree should be printed in vase mode, pay attention to the number of base layers to ensure that the base hole gets printed with no issue.
The base should be printed normally without supports
Warning: trying to persuade the lights to fill the tree evenly instead of turning into a lump in the middle can prompt bouts of seriously un-festive swearing
Real warning: i uploaded the wrong tree model by mistake (right shape but very small), it has been fixed on the 6th of december at 19:15 thanks to NMGMarques' comment, anybody who downloaded it before can resize it in the slicer or download again the tree portion. Sorry
The author hasn't provided the model origin yet.