First problem is that you planted a tree in december, a tree needs time to get established before a harsh winter.... Another issue might be that the roots are still bound by burlap or wire... Make sure the roots are free from any obstructions. If the roots are clear it is most likely just winter stress.... Don't cut of branches until either they become brittle and are clearly dead or they don't produce new leaves next spring..... You could always just return the tree to the nursery because most places have a 2 year guarantee.... If not give it time and see how it does. Hope this helped