This is a pic I found in Hinkle’s photostream, which he took at a convention, so I don’t know who actually built the trees (somebody German, apparently):
https://www.flickr.com/photos/kevinhink/10635048095/in/faves-8994372@N04/
Had I made it to Philly, I would’ve taken four of them along with me. They look good, you can adjust the trunks to whatever height you like (I thought they looked better shorter), you can adjust the size of the tree and control the rate at which you widen it towards the bottom. I found that after more than 5 stems stacked on a stud they started to look unnatural though.
For me the limiting factor was actually the stud-on-4-sides bricks, I used all the dk bley ones I have. (I’m sure I have some in black too, but they’re not sorted out right now, so I have no idea how far they’ll go.) Buying them in black or bley on BrickLink is expensive.
Getting them to stay together is also miserable. The stems never have good clutch power, I tried putting 1-stud round plates on the bricks, but it didn’t help. Once I got them set up and in place they were fine, but you can assume after tranporting them anywhere that you’ll be rebuilding them, and that rebuilding them will involve a lot of accidentally knocking off one branch while you’re putting on another one, which will involve a lot of cursing.
Originally I used all the stems I had on those four trees, but the one didn’t look good so I scaled it back, and with the extras I made smaller trees. I’m not sure I have a pic anyway but I’ve seen them multiple times, you take two brown cones on either end of a brown umbrella stand as your trunk, and then stack any number of stems (I made mine in the range of 10-15) vertically and invert them. Skinny pine tree. They look good, and important if you have bigger trees around or train tracks that makes sticky-outiness an issue, they fit in easily anywhere.
I made 4 of them with the leftovers and then 4 more with additional stems I found in my nephews collection, I’d like to make a ton more.