foreach my $file (@files)
{
    my $outfile = "$file.tre";

    open(IN,   '<',  $file)    or die $!;
    open(FILE, '>>', $outfile) or die $!;

    while (my $tree = <IN>)
    {
        next unless /Tree mixture/;
        $tree =~ s/Tree mixtureTree=//;
        print FILE $tree;
    }

    close FILE or die $!;
    close IN   or die $!;
}