module Tree:sig..end
type ('a, 'cmp) t 
Tree.t contains just the tree data structure that a set is based on, without
      including the comparator.  Accordingly, any operation on a Tree.t must also take
      as an argument the corresponding comparator.include Creators_and_accessors2_with_comparator
val sexp_of_t : ('a -> Sexplib.Sexp.t) ->
       ('cmp -> Sexplib.Sexp.t) -> ('a, 'cmp) t -> Sexplib.Sexp.t