Class Six Climb

A tree 4,200 meters high! That's a bit more than two and a half miles, for those who don't use the metric system. It stands unique in the galaxy. It has never been climbed, not by native, human, or alien.
The climb will be tough for three human misfits. Straight up, gripping the bark, and occasionally coming to a branch upon which to rest. But this tree is so dissociated from the ground that the branches have developed their own separate ecosystems!