Add test cases to multiple test sets

Yes, do the following:

1. Go to Testing > Test Cases
2. Filter the test case list appropriately
3. Select the checkboxes for the ones you want
4. Then use Tools > Add to Test Set
5. Select the test set and click the button to add to the test set.
6. Then repeat steps 4-5 for the other test sets.

Thanks David, i'm aware of that way of adding to test set from test case view, however we have a lots of test sets (up to hundreds), repeating those steps to add to each test sets will take too much time, anyway we can select multiple test sets to do it at once?