Decidable equivalence for TreeSet

instance Std.TreeSet.instDecidableEquivOfTransCmpOfLawfulEqCmp {α : Type u} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] {t₁ t₂ : TreeSet α cmp} : Decidable (t₁.Equiv t₂)