∀ {α : Type u} {β : α → Type v} [inst : Ord α] [inst_1 : SizeOf α] [inst_2 : (a : α) → SizeOf (β a)]
  (treeMap : Std.DTreeMap.Internal.Impl α β) (range : Std.Roi α),
  sizeOf { treeMap := treeMap, range := range } = 1 + sizeOf treeMap + sizeOf range