It's important to know the name of the tree, but if you only bought it a week ago and it's as bad as you say, take it back for a refund. No point is killing yourself over a half dead tree someone else should have taken care of. Plus without knowing what's wrong with it, just throwing names of chemicals at you won't help anything and could do worse damage. Next time you want to buy a tree at least find out what it is first, do a little research about what it needs and whether or not you can supply it (enough light, temperature, humidity, etc. etc.) and how to take proper care of it from the minute you get it home.