<select id="select_opt" name="select_opt">
<optgroup label="foo">
<option value="1">Option 1</option>
<option value="2">Option 2</option>
<optgroup label="foo.foo">
<option value="foo1">Foo 1</option>
<option value="foo2">Foo 2</option>
</optgroup>
</optgroup>
<optgroup label="bar">
<option value="3">Option 3</option>
<option value="4">Option 4</option>
</optgroup>
</select>