there's no better one i can see in unicode, other than that the classic CVS style thing... which i can't find anywhere, and nearest i find is the reverse of this symbol in the cyrillic "ch": Ч

ah there is a close one, some strange symbol for 2: ߂

oh yes, there is an old school notation from books §

but yeah, for something to represent sections of a tree the folder is the best in all unicode probably, plus you can represent it being opened as well with the open form (second one you put there)