Hi

If you search for "root" in http://docs.wxwidgets.org/trunk/classwx_tree_ctrl.html you'll find

wxTR_LINES_AT_ROOT: Use this style to show lines between root nodes. Only applicable if wxTR_HIDE_ROOT is set and wxTR_NO_LINES is not set.

wxTR_HIDE_ROOT: Use this style to suppress the display of the root node, effectively causing the first-level nodes to appear as a series of root nodes.

So this is what that looks like

#!/usr/bin/perl --
use strict;
use warnings;
use Wx;
use Wx::Perl::TreeChecker;
my $frame = Wx::Frame->new( undef, -1, 'Wx::Perl::TreeChecker' );
my $tree = Wx::Perl::TreeChecker->new(
    $frame, -1,
    [ -1, -1 ],
    [ -1, -1 ],
    Wx::wxTR_DEFAULT_STYLE()
    | Wx::wxTR_HIDE_ROOT()
    ^ Wx::wxTR_LINES_AT_ROOT()
);
if( $tree ->IsEmpty ){
    $tree -> AddRoot('/');
}
my $root = $tree->GetRootItem;
for my $ix (1..10){
    my $id = $tree->AppendItem ($root, "noot $ix");
    $tree->AppendItem ($id, "$_ noot $ix") for 1..3;
}
$tree->ExpandAll;
$frame->Show(1);
Wx::SimpleApp->new->MainLoop;
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In your code change the constructor

    $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()
    );
[download]

and modify _populate_tree

            if( $tree ->IsEmpty ){
                $tree -> AddRoot('/');
            }
            my $root = $tree->GetRootItem; 
            my $stream_id = $tree-> AppendItem( $root, $stream  );
            _populate_tree($tree, $stream_id, $data->{$stream});
[download]