Not something you see every day, though I know it happens and have been told about alders growing out of hawthorns in a similar manner to this. Really cool, to be honest. The (epiphytic?) birch (Betula pendula) featured in the below images is, every few years, pruned back, so that its chances of surviving in the oak are better. However, as you’ll see below, one wayward root has done something very awesome!