$data = [
    ["Data_ID", "Condition", "Filename"],
    ["treat1", "treat", "MB-1.counts.txt"],
    ["treat2", "treat", "MB-2.counts.txt"],
    ["control1", "control", "NC-1.counts.txt"],
    ["control1", "control", "NC-2.counts.txt"],
];
$file = fopen("test.csv","w");
foreach($data as $line){
    fputcsv($file, $line);
}
fclose($file);