Here's a pic of our carved Christmas tree cake. Although it looks a bit difficult it was actually quite simple to make once we broke it down. The hardest part of making this cake was going back to high-school math to calculate the angles (yes, my teachers were right when they told me 'you'll use this again!").
Its a three-tier cake with each tier carved at an angle, covered in fondant, and stacked using pillars extending above the tiers (we wrapped the pillars in red fondant). The cake is sitting on a base of styrofoam draped in red fondant for the tree trunk.
Anyone who knows my decorating methods will recognize my favorite part of this cake - the little gumpaste figures under the cake. I can work on these little things all day!