Wow.
(Here are the cupcakes, in case you've forgotten. They're cute, too.)
You'll need icing decorating tips and, of all things -- ice cream cones. Unlike the cupcakes, the cones are cut in half, then fixed to the side of the cake.
Go here for decorating instructions, and the recipe for the cake. This video, on making the Christmas Tree cupcakes, helps too. (The link to the cupcakes recipe is here.)
Wouldn't these be pretty on your holiday dinner table?
(This also ran on the Christmas Goodies blog --
lots of holiday cooking ideas you might enjoy.)