Question

21.If you don't rest, you will be ill

-> Unless...........................................

22.This tree won't grow if there no water

-> Unless.....................

Answer 1

21. If you don't rest, you will be ill.
-> Unless you rest ,you will be ill
22. This tree won't grow if there no water.
-> Unless this tree no water , there won't grow

Answer 2

 21. If you don't rest, you will be ill.

     ->  Unless you rest , you will be ill.

 22. This tree won't grow if there no water.

     ->  Unless there is water, this tree won't grow.