If u want heat i would suggest a catalytic heater such as this, no odour, can get different sizes, they give off lots of heat and they run off propane bottles and if you get a few small bottles they are fairly light and easy to haul up a ladder. Something like this
http://www.landbigfish.com/images/store/PS-5033-751.jpg but if you want a fire so you can cook, i would suggest just bringing a lunch cause i wouldnt have a fire that high up now as for if the fire would spook them, well if your stuck in the woods you know how they say "keep the fire big cause it keeps the animals away" cause the smoke does signal danger, be it humans or forest fire, but i have built a fire on the ground where i was sitting for the day cause it got way to cold and i still seen lots of game, but the wind was blowing the smoke away from the area i was watching.