Some kind of Japanese maple would be a good choice. You can also check out Hydrangea trees (unique, pee gee, etc.)

Japanese maples are beautiful (and expensive), they are also deer candy. So if you have any kind of deer problem, you might want to try something else. The tree hydrangeas don't seem to be as attractive to the deer. A redbud might work, though they do like a bit of sun and might get too big (reaching for light) in total shade.

Thank you both for the tips!

This goes to show how local deer preferences are, because in my area, while Japanese maples are sometimes damaged by deer, they definitely not "deer candy." I do cage them in the winter and spray them in the summer, but I have to do that with all immature trees and shrubs, against gnawing critters as well.

Also, as to cost, I purchased several small Japanese maples on eBay for under $20 each, and have also gotten a few free seedlings at plant swaps. To me they are worth the effort since they are beautiful year round.

Yes, interesting what regional differences there are. The deer have never damaged my Bloodgood Japanese Maple. The Japanese beetles on the other hand, find it delectable.

Yeah, I have that problem too. Why can't deer like Japanese beetles? Then I'd be happy!

Jayco, what a great image that is. If only.

You mention "small tree that's not larger than 6 feet", but I'd like to also encourage you to look for shrubs that can have their lowest branches removed to resemble a miniature tree.

Any of the larger rhododendrons can be grown that way (don't use azaleas though, otherwise they look so silly being "poodled"), as could a Florida anise-tree, VIrginia Sweetspire, etc., enkianthus is amazing.
\ I'm sure there are others there locally that are popular that could be trained that way.