Delphi Help에 나오는 내용입니다...

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;

//첫번째 레벨입니다...

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;

//두번째 레벨추가입니다...