We had a Fiber Optic Christmas Tree at the office, and the fit between the 'trunk' of the tree and the base where the light source was installed was absolutely terrible, with nearly 2mm of slop on what was an already far to narrow base.  This resulted in the tree falling over nearly every time someone walked past it. 

This part is designed to be printed in TPU and is a sleeve that goes between the trunk and the base to improve the fit to a nice, snug one.  the sleeve just slides on the trunk of the tree and then the whole assembly slides into the base.  

The TPU won't deform under the lights, and there should be just enough flex to get a snug fit without having to force anything.

Judging by the base of the tree, there are a number of different configurations of tree that use this base... so, maybe someone out there will find this useful, too.

STEP file is included in case anyone wants to remix.

I recommend printing in TPU or flexible PLA and using staggered inner seams and scarf joints all around to eliminate the seam artifacts. The main body is very thin (only 2 perimeters in total), so any seams will be very noticeable and may result in tearing.

Enjoy!