Meanwhile, I've been prompted to reveal the answer to the tree poser below.
Though I had a few guesses emailed and tweeted to me, it seems the puzzle stumped everyone, and no one twigged - sorry couldn't resist that!
If you've seen the movie The Lord of the Rings, you'll have seen it as the party tree, under which Bilbo Baggins celebrates his eleventy-first birthday. You can see it at Hobbiton, near Morrinsville, New Zealand.