I’m not sure about posting this as an answer, since you are clearly
a (HTML) comment.
If I were a mod,
I could see deleted comments on SE
The opposite tree refers to
the DOM tree (letters of ”mod” reversed), which contains the document’s structure. A comment’s job is often to make that structure easier to understand.
When I read between the lines
of the source code to this puzzle, I notice that there is actually a html comment between lines 1 and 2,
Which is, of course hidden, (or invisible as the title suggests) unless I do exactly that.