One of the huge trees on the hillside above Balmoral on Sydney Harbour, its upper branches look much like the other gum trees: huge arms reaching to the sky. It is well leafed out, with smooth bark, in greys and - once you look - many other colours. But its roots are growing in cracks between massive rocks. It clings to the hillside with what looks like the barest of supports, but in fact this "Rock Climber" is massive and sturdy, confident in its rocky anchor.