src/lay/modules/tree.js
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]);
      }
    }
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]);
      }
    }
执行伸展