If you see what looks like pineapple tops floating in the waters of Canada's Lake Simcoe, beware. They might look innocent enough, but this plant can be dangerous to swimmers, reported CBC ... Does anyone know of a eastern tree, suitable for zone 6, that has an interesting winter silhouette?

Context Explanation

I like the look of a black gum a few streets over, but I want to make sure that I do't over-look any other, possibly nicer ones, as this will probably be the last tree I ever plant. Thanks.