Obviously, there are trees. But speaking phylogenetically, trees aren’t a thing. Some things that are trees evolved from things that are not trees and other things that are trees evolved into things that aren’t trees. Confused? This might clear things up.

“Trees” are not a coherent phylogenetic category. On the evolutionary tree of plants, trees are regularly interspersed with things that are absolutely, 100% not trees. This means that, for instance, either:

The common ancestor of a maple and a mulberry tree was not a tree.
The common ancestor of a stinging nettle and a strawberry plant was a tree.
And this is true for most trees or non-trees that you can think of.

More: There’s No Such Thing as a Tree