What is this intimidating specimen?

So I’ve got this plant growing that I’ve just let go wild as an experiment. It’s younger than. The Baileyana Purpurea and Betula Pendula either side of it.

It pops up around my place from time to time like a weed, but grows into a tree pretty quick.

Ive got my suspicions but keen to get Reddit’s thoughts on what it could be! I haven’t seen it flower yet but there are these buds/bulbs showing for the first time.