Here's a side-by-side of the orginal tree and the "winterized" one. The leaves on the snowy tree have a multilayered texture applied...I will upload them soon so you can mess around with it. The snow on the branches was made by duplicating the tree, then setting leaves to zero, so I just had the trunk and branches. Then I applied the "iceberg" preset under water and liquids. I offset the tree .15 BU up and then moved is slighty away from the camera so the trunk would not have white gunk all over it.