get specific taxonomy below taxonomy in custom module in drupal 7

$machine_name = 'companies';
  $v = taxonomy_vocabulary_machine_name_load($machine_name);
  $terms = taxonomy_get_tree($v->vid);
  foreach ($terms as $term) {
    $options[$term->tid] = $term->name;
  }
  //return $options;
print_r( $options);exit;