Isn't XML already a tree? Joke aside, graphs are far from being trivial to represent as a data structure, and their use are so various that you can hardly edit

Isn't XML already a tree? Joke aside, graphs are far from being trivial to represent as a data structure, and their use are so various that you can hardly edit a graph using text alone. Even a visual editor would require to be tailored to different work you do with graphs.