Preheat the oven to 350°F (175°C) and line a cupcake tray with liners.
In a large bowl, cream together the sugar and butter until light and fluffy.
Add eggs one at a time, mixing well after each addition, then stir in the vanilla extract.
In a separate bowl, whisk together the flour and baking powder, then gradually add it into the wet mixture, alternating with the milk.
Spoon the batter into prepared cupcake liners, filling each about two-thirds full.
Bake for 18 to 20 minutes or until a toothpick inserted into the center comes out clean.
Let the cupcakes cool in the tray for 5 minutes before transferring to a wire rack to cool completely.
Once cooled, frost with green buttercream and decorate as desired to create a Christmas tree look.