Decidable equivalence for TreeMap

instance Std.TreeMap.instDecidableEquivOfTransCmpOfLawfulEqCmpOfLawfulBEq {α : Type u} {β : Type v} {cmp : α → α → Ordering} [TransCmp cmp] [LawfulEqCmp cmp] [BEq β] [LawfulBEq β] {t₁ t₂ : TreeMap α β cmp} : Decidable (t₁.Equiv t₂)