Having been in a couple of tree wells, one upside down and one right side up. It happens really fast and even if you have a split second to react, those holes suck you in; it can happen several days after a big dump and its really disorienting. When I was upside down, I did not know it at first, you can't tell by the light and you body is generally suspended...so its natural to wiggle around to see if you can get yourself out, but as the snow is caving in around you, you are already breathing hard, choking on pow, you heat up instantly and easily panic...especially if you don't know if anyone knows you are there. When I was right side up, I was hiking out of a biff, waist deep and hit a bridged tree/hole...completely buried tree and fell through to my neck and luckily was able to get my board under my arms to prevent sinking deeper and eventually able to pack enough snow under me to wiggle out of the hole. When its those conditions you learn to keep a healthy distance from anything that might look like a tree well.