Table Studycourse:
id, coursename, extension_of

1, Law, 0
2, Economics, 0
3, Business Law, 1
4, Macro Economics, 2


How can i populate a dropdownlist with option groups?

It should generate the following html:

<select name="studycourse" id="course">
        <optgroup label="Law">
            <option value="law-business">Business Law</option>
        </optgroup>
        <optgroup label="Economics">
            <option value="economics-macro">Macro Economics</option>
        </optgroup>
</select>