code: function(){
        if(elem.data('spread')){
          elem.data('spread', null)
          ul.removeClass('layui-show');
          arrow.html(icon.arrow[0]);
          a.find('.layui-icon').html(icon.branch[0]);
        } else {
          elem.data('spread', true);
          ul.addClass('layui-show');
          arrow.html(icon.arrow[1]);
          a.find('.layui-icon').html(icon.branch[1]);
        }
      }
docs: 执行伸展