I knit stranded jumpers/sweaters/gansers for myself and wear them any time it's even a little cold. The ones I make are not Fair Isle, which is very specialised, but they are none the worse for that. (Nor are they "Christmas Jumpers"! Good grief.)
I knitted the most recent one in Norwegian because Ravelry didn't have it translated into English and I really wanted that pattern. www.ravelry.com/patterns/library/0611-01-pullover
I don't think the pattern on the OP's jumper is a Christmas tree; I think it might possibly be a fir-cone. The snowflake pattern (which has eight points and is not a snowflake anyway: snowflakes have six) is a traditional Scandinavian pattern and definitely not reserved for Christmas any more than snow is in Scandinavian countries, or come to that spruce trees are only there at Yuletide. And the things on the OPs jumper are crosses, not snowflakes....
Wear it whenever you feel like, OP. Having any garment or doormat or tablecloth or duvet cover only for Christmas is clean daft.