extjs combobox+treepanel节点重复问题

var root = new Ext.tree.AsyncTreeNode({
id: "0",
leaf: false,
text: "",
expandable: true,
expanded: true
});

var loaderMeasureTree = new Ext.tree.TreeLoader({
clearOnLoad: true,
dataUrl: '',
animate: true,
method: 'POST',
preloadChildren: true,
baseAttrs: { uiProvider: Ext.tree.TriStateNodeUI, checked: false }
});

var measureItemTree = new Ext.tree.TreePanel({
animate: true,
root: root,
loader: loaderMeasureTree,
singleExpand: false,
iconCls: "icon-tree",
autoLoad: false,
rootVisible: false,
autoScroll: true,
allowDomMove: true,
height: 300,
frame: true,
collapsed: false,
collapseFirst: true,
border: false
});