The earth is a plane of balance. After all, it spins. Whatever humans do to the earth changes the balance it achieves. It’s the same with birds. I suspect they did this.

You’re looking at two trees growing as one. That’s a rowan, with fruit, on the right, and a hawthorn, without, on the left, high up in the Swiss Jura. They’ve worked it out well. Likely they feed the descendants of the birds that dropped their seeds in a crack in the stone they are growing from. Likely, they feed them in alternate years.