def insert(index, *items)
      inserting(index ... index + items.size) do
        @array.insert(index, *items)
      end
      self
    end
def insert(index, *items)
      inserting(index ... index + items.size) do
        @array.insert(index, *items)
      end
      self
    end
Inserts items.
 @param [Integer] index
 @return [self]