Procedure TForm1.Button1Click(Sender: TObject);
var
MyTreeNode1, MyTreeNode2: TTreeNode;
begin
with TreeView1.Items do
begin
Clear;
MyTreeNode1 := Add(nil, 'Nodo raiz');
AddChild(MyTreeNode1,'Nodo Hijo 1');
MyTreeNode2 := Add(MyTreeNode1, 'Nodo Raiz 2');
AddChild(MyTreeNode2,'Nodo hijo 2');
Add(MyTreeNode1, 'Nodo raiz 3');
end;
end;