Flex: Tree如何展开/关闭一个节点, 并选中其孩子?　如何关闭所有的节点？

_treeOUs.expandChildrenOf(currentOU, true); // 展开目录 

_treeOUs.selectedItem = ou; //选定孩子

_treeOUs.openItems = []; // 关闭所有节点;

expandChildrenOf(item:Object, open:Boolean):void
Opens or closes all the tree items below the specified item.

expandItem(item:Object, open:Boolean, animate:Boolean = false, dispatchEvent:Boolean = false, cause:Event = null):void
Opens or closes a branch item.