20 feet high reaching for cherries.. no way unless you rent a bucket truck

A good producing cherry tree should have plenty of clusters nearer to the ground. I'd pick what is safe to reach... you be the judge of your own safety... and let the birds have the rest.
Do you prune the trees every year? The reason I ask is why did it get that tall in the first place?
There are 2-3 ranges of "dwarf" but non are meant to allow to grow that tall
for picking fruit.
If you really have to have the fruit from the high branches this year you might suspend netting off the ground and cut the branches with a long pruning pole after you have picked the low branches. You might save a few from the high branches that way or just make juice from them.
The pruning would put you ahead for next year if you don't kill the tree.
How do you spray effectivley in a 20 foot high fruit tree?
Is it a self pollenator or do you have another near by?
Good Luck