$(function() {
            var values="";
            for (var i = 0; i < jsondata.length; i++) {
                values=values+"<optgroup label='"+jsondata[i].div+"'>";
                for(var j=0; j< jsondata[i].list.length; j++){
                    values=values+"<option id='"+jsondata[i].list[j].id+"'>"+jsondata[i].list[j].name+"</option>";
                }
                values=values+"</optgroup>";
            }

            $("#main_selectpicker")
              .html(values)
                .selectpicker('refresh');
}
<select id="main_selectpicker" class="selectpicker  show-tick form-control"  data-live-search="true" data-size="15" onchange="get_values(this.options[this.selectedIndex].value)"/>

function get_values(selected) {
...
}