Mega tree cement base help

I am planning on cementing a pvc sleeve into the ground that I will slide my mega tree center pole into. The center pole will be 1 1/2" black iron pipe and the pvc sleeve will be 2" pvc.

My mega tree will be about 14 feet tall. How deep do you think I need to bury/cement the sleeve into the ground? 4 feet? 5?

Thank you.