TreePanel add children problem

Hi All,
i have this

Code:

---

    var tree = new Ext.tree.TreePanel({
        id:'treeTypeGraph',
        loader:new Ext.tree.TreeLoader(),
        width:200,
        height:400,
        renderTo:Ext.getBody(),
        root:new Ext.tree.AsyncTreeNode({
            id:'root',
            expanded:true,
            leaf:false,
            text:'Tree Root',
            children:[]
        })
        listeners: {
          render : function( _this) {
          load();
          }
    });

function load(){
    var arrChildrenTreeMP= new Array();
   
    var aNode= new Ext.data.Node();
    aNode.id= "cMP_1a";
    aNode.text= "1 a";
    var attr= new Array();
 attr["code"]="code_n1a";
 attr["desc"]="NODE 1 a";
 aNode.attributes= attr;
 aNode.leaf= true;
 arrChildrenTreeMP[arrChildrenTreeMP.length]= aNode;
 
    var aNodea= new Ext.data.Node();
    aNodea.id= "cMP_1b";
    aNodea.text= "1 b";
    var attra= new Array();
 attra["code"]="code_n1b";
 attra["desc"]="NODE 1 b";
 aNodea.attributes= attra;
 aNodea.leaf= true;
 arrChildrenTreeMP[arrChildrenTreeMP.length]= aNodea;
 
 
 
 var root= Ext.getCmp('treeTypeGraph').getRootNode();
 root.appendChild(arrChildrenTreeMP);
 Ext.getCmp('treeTypeGraph').doLayout();
}

---

but the array does'nt load...what is wrong?

Hi, with this new code
Ext.onReady(function(){
function loadArr(){
var rootNode= new Ext.tree.AsyncTreeNode({
id:'rootT',
expanded:true,
leaf:false,
text:'Tree Root'
})

var aNode= new Ext.data.Node();
aNode.nodeType= "node";
aNode.id= "cMP_1a";
aNode.text= "1 a";
aNode.leaf= true;
aNode.expanded= false;

rootNode.appendChild(aNode);
Ext.getCmp('treeTypeGraph').setRootNode(rootNode);
Ext.getCmp('treeTypeGraph').render();

//rootNode.expand(false, /*no anim*/ false);

}

var tree = new Ext.tree.TreePanel({
id:'treeTypeGraph',
loader:new Ext.tree.TreeLoader(),
width:200,
height:400,
renderTo:Ext.getBody()
,listeners: {
render: function(_this){
loadArr();
}
}
});
});

i have this problem:

Attachment 39647
and if i uncomment this line:
//rootNode.expand(false, /*no anim*/ false);

i receive this error:
Attachment 39648

Can someone help me?
Thanks in advance.