procedure TForm1.DeleteNodesActionExecute(Sender: TObject);
var
  I: Integer;
begin
  TreeView1.Items.BeginUpdate;
  try
    for I := TreeView1.SelectionCount - 1 downto 0 do
      TreeView1.Selections[I].Delete;
  finally
    TreeView1.Items.EndUpdate;
  end;
end;