Why is it when i click practice skill for Basics 1, it covers all vocabulary that i've learned and not only from basics 1?
It's because Duolingo adjusts to you and provides review. There's really no way around it, as it's a "feature" of Duolingo.
If you want to restart a tree, you can go to settings and remove that language, and then, add it back. But, careful. All of your progress will be lost.