Views selective filters show terms hierarchy
I realised the BEF desired option "Nested checkboxes" was missing for all selective filters. Since into  better_exposed_filters_exposed_form_plugin.inc, the missing option depends on :

if ($bef_nested) {
  $display_options['bef_ul'] = t('Nested Checkboxes/Radio Buttons');
}


So I added the following :

/* line 314 */
if ($filter instanceof views_handler_filter_selective) {
  $bef_nested = TRUE;
}
/* line 493 */
if ($bef_nested) {
  //...
  $bef_options[$label]['more_options']['bef_select_all_none_nested'] = array(
    '#disabled' =&gt; !$filter instanceof views_handler_filter_selective &amp;&amp;(!$filter-&gt;options['expose']['multiple'] || !$filter-&gt;options['hierarchy']),


I know this is a very quick hack and should be improved for general use. Alternate proposals are warmly welcome.

Last, I had to patch also Views selective filters handler, resulting in :

case 'HCHY':
  $options = array();
  //get remaining terms tids
  $remaining_terms = taxonomy_term_load_multiple(array_keys($oids));
  $tids = array();
  foreach ($remaining_terms as $term) {
    $tids[$term-&gt;tid] = $term-&gt;tid; 
  }
  //get vocabulary tree
  $anyterm = array_shift($remaining_terms); 
  $tree = taxonomy_get_tree($anyterm-&gt;vid);
  if ($tree) {
    //we flag the terms to avoid displaying them more than once
    $flagged = array();
    //we keep tree items if they match with current selection
    foreach ($tree as $trm) {
      if(in_array($trm-&gt;tid, $tids ) &amp;&amp; !in_array($trm-&gt;tid, $flagged) ){
        //so we always keep its parents displayed
        $parents_all = taxonomy_get_parents_all($trm-&gt;tid);

        if($anyterm-&gt;vid == '3'){//country vocab, Three levels taxonomy
          switch (count($parents_all)) {
            case 3: 
              $parent = $parents_all[1];
              $gd_parent = $parents_all[2];
              break;
            case 2: 
              $gd_parent = $parents_all[1];
              break;
            default:
              break;
          }
          //Add the gd_parent to options
          if(!in_array($gd_parent-&gt;tid, $flagged) &amp;&amp; !is_null($gd_parent-&gt;tid)){

            $gd_parent_depth = get_term_depth($gd_parent-&gt;tid)-1;
            $choice = new stdClass();
            $choice-&gt;option = array($gd_parent-&gt;tid =&gt; str_repeat('-', $gd_parent_depth) . $gd_parent-&gt;name);
            $options[] = $choice;
            $flagged[] = $gd_parent-&gt;tid;
          }   
          //Add the parent to options
          if(!in_array($parent-&gt;tid, $flagged) &amp;&amp; !is_null($parent-&gt;tid)){

            $parent_depth = get_term_depth($parent-&gt;tid)-1;
            $choice2 = new stdClass();
            $choice2-&gt;option = array($parent-&gt;tid =&gt; str_repeat('-', $parent_depth) . $parent-&gt;name);
            $options[] = $choice2;
            $flagged[] = $parent-&gt;tid;
          }
        }

        //last, add the term itself to options
        $choice3 = new stdClass();
        $choice3-&gt;option = array($trm-&gt;tid =&gt; str_repeat('-', $trm-&gt;depth) . $trm-&gt;name);
        $options[] = $choice3;   
        $flagged[] = $trm-&gt;tid;
      }
    }
  }
  $oids = $options;

/*
 * Returns a term depth (https://www.drupal.org/node/886526#comment-7708315)
 */
function get_term_depth($tid) {
  $limit = 5;
  $depth = 0;
  while ($parent = db_select('taxonomy_term_hierarchy', 't') -&gt;condition('tid', $tid, '=') -&gt;fields('t') -&gt;execute() -&gt;fetchAssoc()) {
    $depth ++;
    $tid = $parent['parent'];
    if ($depth &gt; $limit) {
      break;
    }
  }
  return $depth;
}


Both are necessary, usual nested checkboxes from BEF do not work as is. This might be useful for some of you.