Begin by placing the green candy melts into a microwave-safe bowl. Heat them in the microwave on high for 1 minute, then remove and stir. Continue microwaving in 15-second bursts, stirring each time until the candy melts are fully smooth and melted, resembling a glossy, vibrant green mixture.

Once the candy melts are melted, add the sweetened condensed milk and the Creme de Menthe to the bowl. Use a spatula to stir the mixture until it becomes completely smooth and well combined.

Cover the bowl with plastic wrap and leave it at room temperature to cool. Stir the mixture every 5 minutes, monitoring its thickness. After about 20 minutes, the fudge should thicken enough to be easily spreadable.

Prepare a piping bag and fill it with the thickened fudge mixture. Onto a parchment-lined baking sheet, begin piping the fudge into tree shapes. Aim for varied heights for a playful display.

While the fudge is still soft, sprinkle rainbow nonpareils generously over each tree to add a pop of color. Finally, place a gold star sprinkle at the top of each fudge tree.