Tree wells are a natural phenomenon in deep mountain snow. Evergreens basically act as flour sifters, causing snow around the trees to have less density than surrounding snowpack. Backcountry snowsport enthusiasts on ungroomed courses who get too close to these trees drop in (usually head-first) and can't extricate themselves.
About 60% of people who die from snow immersion die in a tree well, according to this helpful video:
I bet this dad got in trouble when he got home and showed this video to the kid's mom:
The best part about the main video is the tag on the end for his team-building business. That's one way to build a team.