Как создать optgroup с label у select?

var select = document.createElement("select");
        select.name="main_select_region";
        //select.className="selectpicker show-tick form-control";
        select.setAttribute('class', 'selectpicker');
        select.setAttribute('data-live-search', 'true');
        select.setAttribute('data-size', '15');

for (var i = 0; i < jsondata.regions.length; i++) {
select.options[i]=new Option(jsondata.regions[i].name, jsondata.regions[i].name);
...