I haven't seen tree-edit mode in vim, I've seen it in emacs for clojure (it was called paredit or sth like that) and I've tried to learn it but couldn't get used to it in a few days. Maybe it would work better for formulas.

There are a lot of "fancy" packages tailored to latex and formulas like vim-latexsuite, that set up place holders that you can navigate around and whatnot.

But even without all that, a very basic thing that you can do is move around the matching pairs of braces (and brackets, and other paired things) using %

If you do not want to move, but only see where the matching brace is, you can "set showmatch" and it will flash the matching brace when your cursor passes through the other one. This is really helpful for writing nested formulas (although a better strategy is to add a lot of newlines and whitespace so that the structure of your formulas is clear).

Even mcedit shows matching braces, that's not tree editing :) That would be editor showing a formula in graphic form and allowing you to jump around on it and add/move around nested parts of it with shortcuts.

The show matching braces thing is not essential. But, barring the visual formula, %-navigation through braces is tree navigation.

But if you have serialized code tree navigation isn't needed, the whole point was to make it graphical.