I have some sounds and words I use with my cats. They understand down, off and back. If they are about to get into trouble I give the a warning "ah, ah, ah" which usually keep them from doing the bad thing they were about to do. The tone of it lets them know how much trouble they are about to get in. If they are really bad I say no then growl at them. When we are eating they get the squirt bottle or a grumble. Sometimes I also use the squirt bottle as a warning. I'll pick it up, clear my throat and jiggle it a little. When training a new kitty we also use a lot of redirection. If we have to correct someone several times and they are being hard headed, they get the time out in their kennel then get ignored upon release.
I trained my cats that they are not allowed near the door when it is opening. There is some tile so it makes a very good boundary. With the kitten he is in his crate if both of us aren't home. Otherwise one of us holds him. He's too young for the squirt bottle, but we used to keep one at the door when we first move here for our older cats. They learned very quickly. Good luck on the Christmas tree. We never get a tree if we have kittens. They are usually over a year old and fully trained by the time they see their first tree. We put it up without decorations and monitor and correct. Usually after a week we can hang the ornaments. We have plastic ones for the bottom and don't use the fish hooks. If your cat really likes chewing you tree, look for live catnip or grass plants at the pet store and redirect him towards those.
I only use my cats names when they are being fed, given attention or calling them for play. Only positives. Never use their name when scolding, punishing, going to the vet or any unpleaseant activity. My cats usually come if I call them, and they are not sleeping.