I should stress "a bit". Actually, looking closer at s-expressions right now (I was writing based on what I remembered), I'd like to flip that statement. S-expressions are just a bit more complex than what I have in mind. Or alternately: they're equivalent under some trivial transformation.
It depends on how you look at things - there are supposedly many different implementations of s-expressions, which support different fundamental data types. The basic idea is simpler. There are no fundamental data types, just nodes. For example a 'bit' is a node which can contain one of two child nodes ('one' or 'zero'). Any tree which represents data in memory on a computer can be expanded down to a collection of bits. Though in a text representation or tree editor the user will generally have collapsed the tree such that they don't see individual bits.
What I have in mind could look more complex than s-expression in a different context though: the text file representation of the trees may have more syntactic sugar than s-expressions in lisp.
The representation isn't significantly different, but the focus is. I'm focusing more on things related to type theory, schemas, how to represent patches/diffs, standardizing parsing/generation and other transforms, etc.