I carry a whistle because I ride alone sometimes. I also fell into a tree well and almost got pinned while riding with friends. They didn't know where I was and I was screaming but nobody could hear me. My buddy started to panic and finally I should hear him and got out. He knew to stop because I yelled just before going in. Because of the height of the snow, the branches are much thicker and longer so they too act as a barrier. Tree wells can vary daily based on wind and snowfall. Just ride with caution. I was riding fast and came over a rise and slid right into the base of it.