Accordion Lists or Grouped List

I am trying to create either an accordion list or a grouped list. I have data that looks like this:

|Group|Test |
|-----|------|
|A |Test1 |
|A |Test2 |
|A |Test3 |
|B |Test4 |
|B |Test5 |
|C |Test6 |

I have the tests being selected in a form with check-boxes where they can select multiple tests. But because there are a large number of tests, the users would like to see them either in an accordion style:

> A
> B
> C

Where you click on the letter and it expands:

- A
Test 1
Test 2
Test 3
> B
> C

Or at least grouped:

A
Test1
Test2
Test3
B
Test4
Test5
C
Test6

Any ideas on how to do this?

Thanks!