function selChange(sel) {
    if (!isFirstLevel()) { return }
    $.ajax({
        type: "POST",
        url: 'http://example.com/ajax_refill',
        data: {'category': sel.val() },
        dataType:'json',
        success: function(data) {

           var select = $("#select"), options = '';
           select.empty();

           for(var i=0;i<data.length; i++)
           {
            options += "<option value='"+data[i].id+"'>"+ data[i].name +"</option>";
           }

           select.append(options);
        }
    });
}