$self -> {treechecker} = Wx::Perl::TreeChecker->new(
        $panel,
        -1,
        [ -1, -1 ],
        [ -1, -1 ],
        Wx::wxTR_DEFAULT_STYLE()
        | Wx::wxTR_HIDE_ROOT()
        ^ Wx::wxTR_LINES_AT_ROOT()
    );