Another problem with your idea (besides the operation of it and the tractor instability) is the inherent difficulty of maintaining bucket tilt (pitch) at various useage heights. You're not going to be comfortable even at 12 ft with the platform pitched 15 - 20 degrees.
Instead, rent a towable trailer mounted manlift. My local Home Depot rents them for under $300 for 4 hours. I own a JLG T350 for tree trimming, barn painting and windmill maintenance. You can substitute a jib crane arm for the bucket if needed. It has auto leveling and outrigger load sensing. Mine is an electric (battery) powered job.
Believe me, just for tree trimming alone, you'll want to got 'out' and 'around' besides just 'up'. And definitely more that 12 feet up. Mine goes to 35 ft for a working height of 40.