There is a lot of work we have to do around the nursery to get ready for winter. The trees we
grow expect, and rely on winter to come, but they are also used to being under the ground, away from the harsh temperatures of the surface during winter. They are also vunerable to animals who will nibble away their cambium, which, if it gets bad enough, will kill the trees. If a tree is small enough, animals will leave you with only a frayed stump.
When planning to keep trees alive over winter, you need to keep these concerns in mind: to keep them protected from animals, and also to keep them in enough mass that the roots don't freeze and kill the plant. In planning for this, you need to take into account the amount of snow you will get. If you put a 6 inch wrap on a tree and there is 2 feet of snow, the wrap is going to be a foot and a half under, leaving the tree exposed. For our nursery stock, we placed as many as we could in the pot-in-pot section, and for the rest, we packed them in with mulch and then wrapped the stems.