A tree well is an unstable hole or depression around the base of a tree. It is formed when low branches prevent snow from filling in around the trunk. A person can fall into a tree well and become trapped, resulting in suffocation. It is extremely difficult to get out of a tree well without help. Stay safe while snowshoeing or skiing in the trees—don't get too close to trees, always go with a partner, and keep your partner in sight. Terrain Traps.