<select>
    <optgroup label="Root 1">
        <optgroup label="Group 1">
            <option>Option 1</option>
            <option>Option 2</option>
            <option>Option 3</option>
        </optgroup>
    </optgroup>
    <optgroup label="Root 2">
        <optgroup label="Group 2">
            <option>Option A</option>
            <option>Option B</option>
            <option>Option C</option>
        </optgroup>
    </optgroup>
</select>

<select id="listingchannelschannel" name="Location" data-bind="foreach: rootTerms">
    <optgroup data-bind="attr: { label: name}, foreach: groupTerms">
        <optgroup data-bind="attr: { label: name},foreach: terms">
            <option data-bind="text: name"></option>
        </optgroup>
    </optgroup>
</select>