Part of survival is preparedness, another part is adapting. If you are venturing off into the woods you should always bring with you an axe, hatchet, or a saw, but you might have forgotten them or lost them. In that case, you will need to use a knife for jobs that generally require a much larger tool. But, it can be done, including felling a standing dead tree. The entire process is demonstrated in this video, along with possible dangers and probably difficulties explained.