I've seen a craft like this before but most time it was done with icing. And most times the children end up with more in them then on the cone tree. So today I opted to use puff paint instead of icing.
The puff paint is easy to make - equal parts of shaving cream and white glue, plus a few drops of green food colouring. I don't have an electric mixer at work so we use a whisk to fluff it as much as possible. I hot glued the ice cream cones on to old, used greeting cards (so they'd be easy to carry home).
Then paint, paint, paint to cover the cone.
The children then could decorate their trees with sparkles and shaped confetti.
The sparkles fell like snow onto the trees.