Separate the dough into thirds. To ⅓ of the dough, knead in a few drops of green gel food coloring until your desired color is achieved.
On a clean work surface, roll the green dough out to an even ¼ inch thickness. Use a mini tree cookie cutter to cut out several trees. Re-roll out the excess dough and continue cutting trees until all the green dough has been used. Carefully stack the tree cutouts on top of one another, being sure to align them as accurately as possible. *Very gently* press the stack to adhere the trees to one other.Create three even stacks of trees. Divide the remaining plain dough into thirds once again (one portion for each stack of trees).
Place these tree stacks in the freezer to firm up, about 10 minutes. Keep each tree stack in the freezer until ready to use for the next step.
Use the uncolored dough to roll out small ropes of dough, as long as your tree stacks, and about ¼ inch thick.
Remove the tree stacks from the freezer. To start, press the “trunks” of the trees into one of the ropes, creating a base of plain dough.Gently lay the dough ropes along the crevices of your trees, carefully pressing the dough to fill in the gaps. Work your way around the tree stacks until all of the gaps have been evenly filled in with dough. Once you've put a plain dough rope in each crevice of the trees all the way around, repeat on all of the points of the trees, covering any gaps until all green dough, except for the ends, is covered in plain dough (see pictures above).
Press any extra plain dough evenly on the sides of the dough log to help create more of a circle.Repeat with any remaining tree stacks. Carefully pour sprinkles out onto your clean work surface.Gently roll your cookie logs in sprinkles to coat the outside and to carefully adhere the cookies together without deforming the trees. Wrap the cookie dough logs in cling wrap and place in the freezer to chill.Keep rolls in the freezer until just firm, checking on them every 10 minutes in order to ensure they do not get so hard they crack when cut.Or, keep in the refrigerator for at least 2 hours or overnight. Preheat the oven to 350°F.
Remove the cookie dough logs from the freezer and remove the plasic wrap. Use a sharp knife to slice the logs into individual cookies between ¼ and ½-inch thick. Place the cookies on a parchment paper lined baking sheet. Bake the cookies about 8 minutes, until just barely set. Allow to cool slightly before removing from the baking sheet.
Serve and enjoy!