If not for noise you could probably do well on 20M with the full-size whip. On a second story if you could manage a couple somewhat drooping radials somehow it would really work great. But one just dangling like a tail probably wouldn't be bad either so long as it's all well above ground.
Just the noise, it can be bloody hell.
Another option, utilize the tree and run a EARCHI type endfed via a 9:1 un-un. These are not a true end fed but really an OCF that's fed at a different impedence point than the traditional design, and probably somewhat more immune to the local noise. I have been experimenting with this a bit lately. By the Original EARCHI design it's not a solid performer but 20' or so of feedline (laying on the ground) as counterpoise makes it easy to tune only because of ground loss. On a second story that's hard to do so instead you choke off the feedline and use a separate counterpoise, which must be tuned as half of the OCF that it really always was. But then, after all of the effort you will have something that should perform.
Another option, feed a wire to the tree and a dangling tail via an SGC or radio specific auto coupler. With that you are again in the realm of a vertical in nature and noise issues and also you'll need to choke the shit out of the feedline but if you are fortunate and somehow manage to not have a huge noise problem you will gain much from the ease of operation. I actually use something similar to this at home most of the time. I have a pretty good mass of metal that is connected to the ground side because it's there, but it isn't really necessary.