For an extra layer of flavor, consider adding a pinch of ground ginger or nutmeg to the buttercream. If you don't have piping bags, a zip-top bag with a small corner snipped off will work just as well for the chocolate trees. Melting the chocolate at medium power prevents burning and ensures a smooth consistency. Cupcakes can be made a day in advance. Store in an airtight container at room temperature. Buttercream can also be made a day in advance and stored in the refrigerator. Let soften slightly before using. Make sure all ingredients are at room temperature.