How to get rid of HUGE wasp's next/hive in a tree?

It's always safer to call a professional exterminator.

Best time to spray the hive is at night with a bee spray that has a distance knob

could tey taking a brown paper bag and tying the open end of it to mimick the look of the existing nest since hornets are territorial it could help drive them away along with long spray insecticide or high power wate hose to destroy their nest. I would wait until evening as they seem slower then.

i would call an exterminator. It's not worth the risk.

Wasps and hornets are 2 different insects. Hornets make a paper nest egg shaped. They are bad news. I have killed them using rags and paper dipped in diesel fuel attached to a long pole and torched with a good fire from under the nest. I also put on winter jackets and several pants, hat , gloves and running shoes in case any comes my way. I have also sprayed the nest with diesel fuel and torched it after. If you feel uncomfortable hire a pest control company. I do this on a cold day when they are all inside the nest and never been bitten.

Hire someone to do it. It's worth paying someone that has the right equipment and protection to do it.

Had some going under the eaves in the corner once, I waited until dusk when they were in the nest for the night and sprayed it good in the opening they were using. I did this a couple of nights in a row and never saw them again.

I’ve Done this many times and I was always afraid of being stung. The best time is around sunset or daybreak. Just enough light so you can see the target. When spraying over head I put on a jacket, tie a scarf over my head and put a hat over it. You don’t want them falling in your hair. Red flag wasp and hornet spray is the one of my choice. I think the sprayer is more user friendly. The spray disables them on contact. Make sure the nest is saturated and leave it in place, because it will continue to kill a week later if strays that weren’t in the nest return. Peel off the protective wear before going inside so that you don’t take any that may have landed on you inside with you. I have been stung but never when I was in terminator mode.