Twisty oak

Out for a very cold walk today, especially up where this oak was. Like many such trees it has become very contorted and seems to have lost various limbs over the years. Why some oaks grow like this I don't know - I suppose it might be a particular variety, or maybe some sort of mutation. Or just that until a nearby shelter belt was planted a few decades ago this must have been a very exposed spot.The branches of another tree are intruding a bit in the background.