Looking good so far!
I like the colors and the pattern of the ground, the white grass and lumps of snow.
The tree somehow doesn't make me feel like I'm looking at a winter scene though. The white canopy kinda hints at it, but still it reminds me more of a tree full of cherry blossom than snow. I guess the reason is because these kinds of trees usually lose their canopy by the time winter comes around, and you could see only bare branches with a few stray leaves hanging.
I think that contrasting black or dark grey bare trees would create a more wintery landscape feel, and perhaps there could be snow-covered evergreens (eg. pine) if you want to go for full-canopy trees.
Other than that, icicles and frozen patches of ground could go with this tileset nicely.