They don't actually use trees in the paper though. https://arxiv.org/abs/1912.01412 https://arxiv.org/abs/1912.01412 They express everything in reverse polish

They don't actually use trees in the paper though. https://arxiv.org/abs/1912.01412 https://arxiv.org/abs/1912.01412 They express everything in reverse polish notation, exactly so the transformer network can work on streams and not care about the nesting levels. It's a bit odd that this article doesn't talk about that.