Melt the green candy melts in a microwave-safe bowl. Heat on high for 1 minute, then stir. Continue to melt in 15-second intervals until smooth.

Stir in the sweetened condensed milk and crème de menthe until fully combined and smooth.

Cover the fudge mixture with plastic wrap and cool at room temperature, stirring every 5 minutes until it thickens to a frosting-like consistency, about 15-20 minutes.

Transfer the mixture to a piping bag fitted with a star tip and pipe into festive tree shapes on a lined baking sheet.

Before the fudge sets, sprinkle with rainbow nonpareils and gently press gold star sprinkles on top.

Let the fudge trees set completely at room temperature for at least 30 minutes or refrigerate for 15 minutes to speed up the process.