Maybe we're going too far with these. How about we give them Snow Striding/Snowcrossing/whatever we want to call it and call that enough?
Frost treants appear to be trees, like their deciduous kin, but they are instead evergreen. Their boughs are typically covered with snow, and their eyes glitter with cold malice.
Like other treants, frost treants defend their forests, but their frigid hearts seethe with a hatred of all animal life, especially sentient beings.
That could probably be fleshed out a little. This isn't my strong suit.