Prepare a 9x13-inch baking dish by lining it with parchment paper; put aside. If parchment is unavailable, consult the notes.

In a large saucepan set over medium-low heat, combine butter and marshmallows, stirring constantly with a silicone spatula until melted. Quickly mix in vanilla.

Remove from heat. While the marshmallow mixture is still hot, swiftly incorporate food coloring until you achieve the desired green tree hue. Then immediately fold in the Rice Krispies cereal until evenly distributed.

Spoon the mixture into the prepped dish. Lay another sheet of parchment over the top, pressing down gently but firmly to flatten into an even layer. Allow to cool fully, at least 1 hour.

Lift the parchment to remove the block from the pan. On a cutting board, slice the rectangle in half lengthwise, then cut each half into 6 triangles to create tree shapes. Gently push a pretzel stick into the bottom of each triangle.

Put the white chocolate wafers into a small microwave-safe bowl. Heat at half power in short bursts, following package directions, until melted and smooth. Spoon the melted chocolate into a freezer zip-top bag, snip off a corner, and drizzle over each tree. Immediately decorate with sprinkles. Wait for the chocolate to harden before serving.