use strict;
use warnings;
use XML::Twig;
use Data::Dumper;


my $xml;
{
    local $/ = '';
    $xml = <DATA>;
}

print $xml, "\n";

my $twig = XML::Twig->new();

$twig->safe_parse( $xml );

my $struct = $twig->simplify( 
    forcearray => 1, 
    keyattr => [ qw/id/ ],
#    group_tags => { 'node id' => 'id' }, 
);

print Dumper $struct;

__DATA__
<?xml version="1.0" encoding="ISO-8859-1"?>
<thread id="504929">
<node id="504941">
</node>
<node id="504942">
<node id="504950">
<node id="504964">
</node>
</node>
<node id="504953">
</node>
</node>
<node id="504944">
</node>
</thread>