One study found in the Wilderness and Environmental Medicine Journal had an answer. But first, let’s consider the differences between the snow in each case.
An avalanche victim is typically surrounded by very dense and compact snow as a result of the forces involved with an avalanche. It’s like concrete.
The snow surrounding trees is much different. As we know, the snow crystals of tree wells are typically much larger and have less cohesion, this creates lower density snow with much more air. For a review on the dangers of tree wells, see this article: What to do if you friend is buried in the tree well.
The collected data showed a faster core body temperature drop rate in the avalanche victims vs the tree well victims. The average expected time to hypothermia (35C) was 185 minutes for the avalanche victims and 250 minutes for the tree well victims. There was no significant difference in vital signs.
For a review of the Wilderness Medical Society hypothermia guidelines or the new WMS avalanche guidelines, click here. The paper the this study can be found here: http://www.wemjournal.org/article/S1080-6032(17)30244-2/fulltext