I got the answer of the same, here is the answer if anybody wants,
<td><select class="fieldValue" data-bind="foreach: $root.AvailableFields, value: FieldId, event :{ change: $root.onFieldSelectionChange}">
<optgroup data-bind="attr: {label: FieldGroupName}, foreach: Fields">
<option data-bind="text: HeaderText, value: FieldId"></option>
</optgroup>
</select>
</td>
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