I want to create a box around the last 5 bars. I only want to draw one box on the chart.

I have written this code, but it doesnt work.

// @version=5
indicator("One Box", overlay=true)

var int left = na
if barstate.islast
    left := bar_index-5

top    = ta.highest(5)
bottom = ta.lowest(5)
box.new(left= left ,top= top, right= bar_index, bottom= bottom)

Many thanks