Melt 3 T. butter with 3 cups miniature marshmallows in a heavy saucepan. Stir.
Remove from heat.Add 1/2 teaspoon vanilla and 1/2 teaspoon green food coloring.
Fold in 4 cups Cheerios.
Shape 2/3 cup of mixture in a tree.
Put on waxed paper.Add gumdrop slices for ornaments.
Put the remainder of the mixture in the shape of a star connected by a toothpick for the top.