Preheat the oven to 350 degrees F. Grease and flour a 9 x 13-inch pan. Line the bottom of the pan with parchment paper.
You have to bake 3 cakes, but bake them one at a time, mixing up the batter only when you're ready to bake. For 2 of the cakes, tint the batter green. For the third cake, tint the batter red. Bake each cake until the center springs back when lightly touched, about 45 minutes.
Let the cake cool in the pan for 15 minutes, then invert the cake onto a wire rack to cool. Chill in the fridge for 30 minutes so the cake becomes firm.
Carve and level the cakes: Using plates, bowls, glasses or round cookie cutters to trace around, cut the following: From the two green cakes, cut out 4 rounds: 8 inch, 6 inch, 4 inch, and 2 inch. Then from the red cake, cut out 4 rounds: 7 inch, 5 inch, 3 inch, and 1 inch. Take the round cookie cutter and cut a hole through the centers of the 4 inch, 5 inch, 6 inch, and 7 inch layers. (Save all the scraps for making Christmas-colored cake pop dough!)
Make the buttercream frosting. Measure out 1 cup and tint it red. Tint the rest dark green.
Spread a little green frosting on the cake board, lay down the 8 inch green cake layer, and spread a layer of frosting on top. Add the 7 inch red layer and repeat, taking care not to frost the inside edges of the center hole. Continue stacking and frosting gradually smaller cake layers until you reach the 4 inch layer.
Take the 3 cups of candy and fill the center core of the tree, pressing down a little to compact the candy. Frost the top of the 4 inch layer and continue stacking and frosting until all the layers are stacked.
Once stacked, take a serrated knife and gently carve away the sharp edges of the layers to form a tall cone shape. Apply a very thin "crumb coat" of frosting all over the outside of the cake. Set in the fridge for 30 minutes.
Meanwhile, make the Christmas lights. Melt the Candy Melts. Cut the colored Tic Tac candies in half crosswise. Use a toothpick dipped in the melted candy to attach a Tic Tac to the end of a peanut M and M of the same color (the M and M is the bulb and the Tic Tac is the base). You will need about 40 of these.
To make the star for the top of the tree, trace around a star cookie cutter onto parchment. Pipe an outline of white melted candy, then fill in the shape. Place a lollipop stick in the center and cover with more melted candy. Sprinkle with sanding sugar and let set at room temperature.
Place the green frosting into a piping bag fitted with a number 21 open star tip. Starting at the top of the cake, pipe 3/4 inch long strands of frosting in neat rows around the entire cake, like layers of pine branches on a Christmas tree.
Once the cake is covered, place the red frosting into a piping bag fitted with a number 21 piping tip and pipe draping lines of "tinsel" around the cake. Attach the colored M and M lights directly to the red frosting. Work quickly here, as the frosting will start to form a crust, which can make attaching the decorations difficult.
Take the star and flip it over. Coat the back with white melted candy and sprinkle with sanding sugar. Allow to set. Insert the lollipop stick into the center of the top of the tree.
Classic Vanilla Cake Batter:
Preheat the oven to 350 degrees F. Grease and flour an 8 x 3 inch round cake pan. Line the bottom of the pan with a round of parchment paper.
In a stand mixer, with the whisk or paddle attachment, beat the butter, sugar, and eggs on high speed until light and fluffy, about 2 minutes. Using the tip of a sharp knife, scrape the seeds from the vanilla bean into the mixer bowl. Add the oil to the creamed mixture and combine.
In a small bowl, whisk together the flour and baking powder. Add the flour mixture and milk to the creamed mixture and beat on high speed until the flour is completely mixed, 30 seconds to 1 minute. Scrape the batter into the pan and use an offset spatula to smooth the top.
Bake until a wooden skewer inserted into the center of the cake comes out clean, 55 to 60 minutes. Check after 45 minutes, and if the top is browning too much, tent with foil. Cool the cake in the pan for 15 minutes, then run a metal spatula around the edge of the cake and invert onto a wire rack to cool completely.
Vanilla Bean Buttercream Frosting:
In a stand mixer with the whisk or paddle attachment, beat the butter on high speed for at least 5 minutes, until the butter has lightened in color and is thoroughly whipped. Using the tip of a sharp knife, scrape the vanilla seeds into the butter and beat to incorporate.
Add 1 cup of the sugar and begin mixing on low speed to combine, then beat on high speed for about 2 minutes. Repeat this process 1 cup at a time until all the sugar has been added. Add milk a dash at a time if the mixture becomes too thick or dry. Scrape down the sides as needed and make sure no sugar is visible.
The frosting will last for 1 month in the freezer, 2 weeks in the fridge, and 3 days at room temperature.