Como inserir um item em uma treeview (run time)?

Procedure TForm1.Button1Click(Sender: TObject);
var
MyTreeNode1, MyTreeNode2: TTreeNode;
begin
with TreeView1.Items do
begin
Clear; { Remove qualquer node existente }
MyTreeNode1 := Add(nil, 'RootTreeNode1'); { Adiciona o node raiz }
{ Adiciona um sub item no node adiciona anteriormente }
AddChild(MyTreeNode1,'ChildNode1');
{Adiciona outro node raiz}
MyTreeNode2 := Add(MyTreeNode1, 'RootTreeNode2');
AddChild(MyTreeNode2,'ChildNode2');
MyTreeNode2 := TreeView1.Items[3];
AddChild(MyTreeNode2,'ChildNode2a');
Add(MyTreeNode2,'ChildNode2b');
Add(MyTreeNode1, 'RootTreeNode3');
end;
end;