Root extjs displayed or the control treepicker

createPicker: function () {
        var me = this,
            picker = new Ext.tree.Panel({
                baseCls: Ext.baseCSSPrefix + 'boundlist',
                shrinkWrapDock: 2,
                store: me.store,
                floating: true,
                displayField: me.displayField,
                columns: me.columns,
                minHeight: me.minPickerHeight,
                maxHeight: me.maxPickerHeight,
                manageHeight: false,
                shadow: false,
                rootVisible: false,//去除根节点
                listeners: {
                    scope: me,
                    itemclick: me.onItemClick,
                    itemkeydown: me.onPickerKeyDown
                }
            }),
            view = picker.getView();

        if (Ext.isIE9 && Ext.isStrict) {
            // In IE9 strict mode, the tree view grows by the height of the horizontal scroll bar when the items are highlighted or unhighlighted. 
            // Also when items are collapsed or expanded the height of the view is off. Forcing a repaint fixes the problem. 
            view.on({
                scope: me,
                highlightitem: me.repaintPickerView,
                unhighlightitem: me.repaintPickerView,
                afteritemexpand: me.repaintPickerView,
                afteritemcollapse: me.repaintPickerView
            });
        }
        return picker;
    },