procedure TForm1.Button1Click(Sender: TObject);

var
  MyTreeNode1, MyTreeNode2: TTreeNode;
begin
  with TreeView1.Items do
  begin
    Clear; { remove any existing nodes }
    MyTreeNode1 := Add(nil, \'RootTreeNode1\'); { Add a root node }
    { Add a child node to the node just added }
    AddChild(MyTreeNode1,\'ChildNode1\');

    {Add another root node}
    MyTreeNode2 := Add(MyTreeNode1, \'RootTreeNode2\');
    {Give MyTreeNode2 to a child }
    AddChild(MyTreeNode2,\'ChildNode2\');

    {Change MyTreeNode2 to ChildNode2 }
    { and add a child node to it}
    MyTreeNode2 := TreeView1.Items[3];
    AddChild(MyTreeNode2,\'ChildNode2a\');

    {Add another child to ChildNode2, after ChildNode2a }
    Add(MyTreeNode2,\'ChildNode2b\');

    {add another root node}
    Add(MyTreeNode1, \'RootTreeNode3\');
  end;

end;