code: function(option, data) {
    data = data || option;
    var content = this.customOption ? this.config.renderOption(data) : option.textContent;
    var opt = util.createElement("li", {
      class: "selectr-option",
      html: content,
      role: "treeitem",
      "aria-selected": false
    });
  
    opt.idx = option.idx;
  
    this.items.push(opt);
  
    if (option.defaultSelected) {
      this.defaultSelected.push(option.idx);
    }
  
    if (option.disabled) {
      opt.disabled = true;
      util.addClass(opt, "disabled");
    }
  
    return opt;
  }
docs: Build a list item from the HTMLOptionElement
  @param  {int} i      HTMLOptionElement index
  @param  {HTMLOptionElement} option
  @param  {bool} group  Has parent optgroup
  @return {void}