Position an oven rack in the bottom third of the oven and preheat to 250 degrees F. Line a baking sheet with parchment paper.
Beat together the egg whites and salt in a large bowl with an electric mixer on medium-high speed until foamy. Add the cream of tartar and continue to beat until soft peaks form. While beating, add the confectioners' sugar 1 tablespoon at a time. Continue to beat until stiff peaks form.
While the mixer is still running, add the green food coloring and mix until combined. Put the meringue into a disposable piping bag fitted with a large star piping tip. Holding the bag at a 90-degree angle to the baking sheet, pipe a large star and then two smaller stars on top to create a tree; repeat until all the meringue is gone.
Bake until the meringues are no longer glossy and feel light and dry when picked up, about 1 hour.
Open the oven for a few minutes, then turn it off and shut the door. Leave the meringues in the oven until they are completely dry inside, about 2 hours.
Once the meringues have cooled, dust the tops with confectioners' sugar to resemble snow.
Serve immediately or store in an airtight container.