Melt the white candy melts according to package instructions.
Dip the bottom half of an Oreo cookie into the white candy melts.
Sprinkle the white candy melts with the white sugar crystals while the candy melts are still warm.
Place a single chocolate sprinkle in the candy melts vertically for the tree trunk.
Melt the green candy melts according to package instructions.
Once the green candy melts are melted, transfer them to a Ziploc bag.
Cut a tiny hole in the corner of the bag. Do not cut too large of a hole, because this is how the melted candy is going to come out of the bag.
Pipe a triangle tree on the Oreo cookie making sure the bottom of the tree touches the chocolate sprinkle tree trunk.
Sprinkle some of the Christmas sprinkles on the tree for the ornaments.
Top the tree with a star sprinkle or a star candy.
Allow the cookies to sit for a few minutes so all of the candy decorations dry. It is best to hold the cookie in your hand until the back side of the cookie is dry so it does not mess up when you lay it down.
Either serve the cookies immediately or place them in an air tight container until you are ready to serve them. Be sure to place a single piece of parchment paper between the layers of decorated cookies to keep them intact.