Everything at Durmstrang was about tradition. That included Christmas. And Christmas trees. Namely, the cutting down and hauling in of Christmas trees by fourth years and up.
Without magic.
"Igor, you lazy sod! Get over here and help!"
The first snowball nicked Igor's shoulder; the second splatted against his cloak.
"You've already got it," he pointed out, watching Anna and the others struggle with the heavy ropes affixed to the felled trunk. "What's left for me to do?"
"Get over here or I'll paste you to this goddamned tree with a Sticking Charm!"
Igor snorted. "You wouldn't dare."
She did.