Heat oven to 200°F.
Line two baking sheets with parchment paper and set aside.
In the bowl of a stand mixer fitted with the whisk attachment place the egg whites, cream of tartar and pinch of salt.
Whisk the egg whites until soft peaks form.
Add the green food coloring as needed.
Gradually add sugar, a tablespoon at a time, whisking well between each addition, until sugar dissolves.
Place the mixture into piping bag with a large round tip.
Pipe cookies into tree shapes on the prepared baking sheets.
Sprinkle cookies with multi color sprinkles.
Place the star sprinkles on top.
Bake in preheated oven for 2 hours.
After 2 hours, turn the oven off.
Open the door slightly and let sit in the oven for additional 2 hours.