Based on http://www.bioperl.org/wiki/HOWTO:Trees#Reading_and_Writing_Trees, it seems you need something like:

open my $fh, '>', 'filename' or die $!;

while ( my $tree = $treeout->next_tree ) {
    for my $node ( $tree->get_nodes ) {
        printf $fh "id: %s bootstrap: %s\n", $node->id || '', $node->b
+ootstrap || '', "\n";
    }
}

close $fh or die $!;
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Hope this helps!