In this code

(functions.php

else if($type == 'transaction') {
    $opt[0] = __('All', 'beta');
    $opt[1] = __('Sell', 'beta');
    $opt[2] = __('Buy', 'beta');
    $opt[3] = __('Rent', 'beta');
    $opt[4] = __('Exchange', 'beta');

  } )

  how can I put transaction subcategories?

No such functionally exists, use attributes plugin or some different alternative

OK thanks