In all the years we’ve lived in San Francisco, we’ve never had a tree. We always go home for Christmas, we’ve reasoned, so what’s the point? But we’ve missed it, and home is sort of like an electron or whatever — it’s wherever it is when you notice it, but it could very well be someplace else simultaneously. Plus, this wee one’s not even three feet tall, and was less than $20. How could we resist?