Feature Request: Tree-structured editing instead of linear editing.

[stustd]

Most program structures are hierarchical (refinement of concepts and detail), and managing growing software complexity is best served by knowing and organising the concept level you're dealing with. Following that paradigm, the Leo Outline Editor ( https://leo-editor.github.io/leo-editor) is a very useful and productive example. Wouldn't it be nice if Marimo would provide a similar, tree-structured, editing experience where details, branching out from their higher level concepts, can be folded so that views of same-level concepts can be maintained?