Linear tree in Flex

<mx:Script>
    <![CDATA[
        private function openAllNodes():void {
            tree.openItems = dp..node;
        }

        private function closeAllNodes():void {
            tree.openItems = [];
        }
    ]]>
</mx:Script>

<mx:XML id="dp">
    <root>
        <node label="Parent 1">
            <node label="Child 1" />
            <node label="Child 2">
                <node label="Grandchild 1" />
                <node label="Grandchild 2" />
            </node>
            <node label="Child 3" />
            <node label="Child 4" />
        </node>
    </root>
</mx:XML>

<mx:ApplicationControlBar dock="true">
    <mx:Button label="Open all nodes" click="openAllNodes();" />
    <mx:Button label="Close all nodes" click="closeAllNodes();" />
</mx:ApplicationControlBar>

<mx:Tree id="tree"
        dataProvider="{dp}"
        showRoot="false"
        labelField="@label"
        width="200" />

      

        
        
        
      

    

Unless I selected another parent list, the child or next list should be in a disabled state.

I click "Child 1" then only "Child 2" should be able to select.

Please help me.