On a scale from most to least advanced, you could use jut a really, really long chainsaw, or a two-man saw, but that would require fancy things like electronics and metal to make. You could just use an axe, but that would take days, if not weeks of constant chopping. You could maybe expedite this by having multiple people working on one tree, and having it be a big social event, like a tree-hunt. You could maybe use fire, but I’m sketchy on this one, because I’m not really sure how well you could contain the fire to keep the entire tree from going up. Another potential problem with fire is that that past the bark, it’s going to be living wood, which doesn’t burn so well. Whether that would help or hurt the fire effort, I’m not sure. But the easiest possible way I can think of to cut down such a tree is to circumvent the tree entirely. You dig a few holes down on one side of the tree, and chop though the roots, not the trunk. Depending how far down you dig, the roots would be both much thinner than the trunk of the tree, and somewhat fleshier, making them easier to cut through. The second part of Operation: Timberrrrrrr would be to have someone chuck a lasso, or something approximating it, up to the top of the tree-trunk, and tie it on. Then you do that a few more times, and round up a whole messload of people to pull on the ropes from the side opposite that of all those roots you chopped through (and be standing off to the sides somewhat, so they don’t get smushed when it falls). Hopefully, the roots have been weakened enough so that you can pull it to the point where gravity takes over, and it’s own massiveness rips it straight out of the ground. Then you just cut the few roots that weren’t torn, and cart it off to camp! I’m not sure if this whole plan is actually any easier than just cutting it down, because I don’t know how deep the roots of this hypothetical tree would go, or how big they would be. It might take just as much, or more effort doing the whole roots-n’-ropes thing. But it’s certainly a much more interesting way of doing it!