Preheat your oven to 225°F (110°C) and line a baking sheet with parchment paper.

In a clean mixing bowl, whisk egg whites on medium speed until foamy, about 2 minutes.

Add cream of tartar to the whipped egg whites, then increase to high speed and whisk until soft peaks form (2-3 minutes).

Gradually add granulated sugar, one tablespoon at a time, while whisking at high speed for about 8-10 minutes until stiff peaks form.

Gently fold in vanilla extract and green gel food coloring until just incorporated.

Transfer meringue to a piping bag and pipe tree shapes onto the prepared baking sheet.

Bake in the preheated oven for 1 hour and 30 minutes without opening the door.

Turn off the oven, leave the door slightly ajar, and cool the meringues inside for 30 minutes.