[Bruce is vaguely familiar with Norse mythology and what it holds, though its been a while since he's heard the stories. Still, its enough for him to understand where Tony is getting at.
He nods, to both Howard and Tony, before adding his own theories.]
Perhaps our world is a branch - from another branch. Saw off a branch and it can be a tree of its own, after all. [In that way, the connection still made sense. Perhaps the 'Yggdrasil' in Asgard is just a branch of the bigger Yggdrasil? Who knows.
But with that said...] Isn't there something in the myths about a serpent, too? A serpent and a tree, like Yggdrasil.