"Juletrefest", literally "Christmas tree party", is a traditional Norwegian party for children, often held during advent, or sometimes between Christmas and New Year's Eve. It is usually arranged by the school or the kindergarten, and can thus be said to be a julebord for children, though it's normally not a dinner party. As the name indicates, there will usually be a Christmas tree present, and popular activities include walking around the tree in one or more concentric circles, singing Christmas carols, and eating rice pudding. There can also be other party games and eating of cake or various kinds of Christmas cookies (about which more later). Often, one of the parents not present at the party will dress up as Santa and pay a short visit to hand out candy and/or mandarins.
It is not traditional in Norway to fool children into believing in Santa, though at smaller family gatherings the father of the house will sometimes excuse himself to step outside for a moment, and by a weird coincidence Santa will always show up shortly afterwards. However, the children are usually not very old when they start questioning the appearence of Santa, wearing dad's slippers, when dad just happens to be outside. In such cases, it is good sport to have an accomplice put on dad's slippers and dress up as Santa, so dad can come back inside while Santa is still in the room.
This article ended up a bit shorter than I had imagined, but I can't think of much more to say on the topic. Looking back, I have real trouble seeing how any juletrefest could possibly last for more than three quarters of on hour.