how to get the selected node ID in tree?

Dear friends,

        I write a tree in my view just like this, when I select different node, I want to show different layout by the node ID. but now my problem is I can not get the selected node ID, can any friends help with this ?

        No matter I use getparameter or getSource , I can not get the selected node ID.

my code：

var oTree =  new sap.ui.commons.Tree("tree",{

  selectionChange:function onMenuTreeClick(oControlEvent){

               var selectedId = oControlEvent.getParameter("nodes");

               // var selectedId = oEvent.getSource();

                    switch(selectedId){

                    case "node1":

                    break;

                    default:

                    break;

                    }

                   }

  });

var oNode1 = new sap.ui.commons.TreeNode("node1", {text:"Sale Order", icon:"images/folder.gif", expanded: true});

  var oNode2 = new sap.ui.commons.TreeNode("node2", {text:"Billing", icon:"images/folder.gif", expanded: true});

  var oNode3 = new sap.ui.commons.TreeNode("node3", {text:"Inter company billing", icon:"images/folder.gif"});

  var oNode4 = new sap.ui.commons.TreeNode("node4", {text:"Normal billing", icon:"images/folder.gif"});

  var oNode5 = new sap.ui.commons.TreeNode("node5", {text:"Delivery", icon:"images/folder.gif"});

  var oNode6 = new sap.ui.commons.TreeNode("node6", {text:"Purchase Order", icon:"images/folder.gif"});

  var oNode7 = new sap.ui.commons.TreeNode("node7", {text:"Invoice", icon:"images/folder.gif"});

  oNode1.addNode(oNode2);

  oNode1.addNode(oNode5);

  oNode2.addNode(oNode3);

  oNode2.addNode(oNode4);

  oNode6.addNode(oNode7);

  //add Tree Node root to the Tree

  oTree.addNode(oNode1);

  oTree.addNode(oNode6);

Best Regards,

Zhang