∀ {α : Type u} {cmp : α → α → Ordering} {t : Std.TreeMap α Unit cmp} [Std.TransCmp cmp] [inst : BEq α]
  [Std.LawfulBEqCmp cmp] {l : List α},
  List.Pairwise (fun a b => ¬cmp a b = Ordering.eq) l →
    (∀ a ∈ t, l.contains a = false) → (t.insertManyIfNewUnit l).size = t.size + l.length