ExtJs树展开到指定节点

 var new_params = {            type: "getProject",            pid: Ext.getCmp('tzmc').value        };        Ext.apply(_store_TGrid_xmb_xmb.proxy.extraParams, new_params);        _store_TGrid_xmb_xmb.load({        callback: function(records, options, success) {        var root = _grid_TGrid_xmb_xmb.getRootNode();        root.expand();        root.eachChild(function(node) {        node.expand();        node.eachChild(function(node2) {            node2.expand();            node2.eachChild(function(node3) {                 node3.expand();            })       })    })   }      })