∀ {α : Type u} {β : Type v} {γ : Type w} {cmp : α → α → Ordering} {t : Std.TreeMap α β cmp} {f : α → β → Option γ},
  (Std.TreeMap.filterMap f t).toList = List.filterMap (fun p => Option.map (fun x => (p.1, x)) (f p.1 p.2)) t.toList