If you can sustain the activity for more than 10 minutes it is by definition not high intensity.
I like 30s on 60s off for 10-15 rounds.
You can refer to this article for examples on HIIT protocols:
https://startingstrength.com/article...r_reynolds.pdf
As a side note our trainers have burnt up more than one treadmill by doing this so while effective it may very well shorten the lifespan of your treadmill...