js 异步加载 tree 采用ajax技术，在点击tree的node以后从数据库中读取其下面的分支并进行显示，适合于tree数据量较大的情况下异步从数据库中查询并显示于tr-js asynchronous load tree using ajax technology, click on the node after the tree from the database to read the following branches and showed that the amount of