wordpress - menu de taxonomias nos CPT

<?php
// MENUS DROP DOWN NOS PAINÉIS DOS POSTS
/* CPT Produtos */
add_action( 'restrict_manage_posts', 'my_restrict_manage_posts' );
function my_restrict_manage_posts() {
global $typenow;
if ($typenow == 'produtos') {
$filters = array('linha');
foreach ($filters as $tax_slug) {
$tax_obj = get_taxonomy($tax_slug);
$tax_name = $tax_obj->labels->name;
echo "<select name='$tax_slug' id='$tax_slug' class='postform'>";
echo "<option value=''>Mostrar $tax_name</option>";
generate_taxonomy_options($tax_slug,0,0);
echo "</select>";
}
}
/* CPT Serviços */
elseif ($typenow == 'servicos') {
$filters = array('tipo');
foreach ($filters as $tax_slug) {
$tax_obj = get_taxonomy($tax_slug);
$tax_name = $tax_obj->labels->name;
echo "<select name='$tax_slug' id='$tax_slug' class='postform'>";
echo "<option value=''>Mostrar $tax_name</option>";
generate_taxonomy_options($tax_slug,0,0);
echo "</select>";
}
}
/* CPT Cadastros */
elseif ($typenow == 'cadastros') {
$filters = array('clientes', 'fornecedores');
foreach ($filters as $tax_slug) {
$tax_obj = get_taxonomy($tax_slug);
$tax_name = $tax_obj->labels->name;
echo "<select name='$tax_slug' id='$tax_slug' class='postform'>";
echo "<option value=''>Mostrar $tax_name</option>";
generate_taxonomy_options($tax_slug,0,0);
echo "</select>";
}
}

/* CPT Documentos */
elseif ($typenow == 'documentos') {
$filters = array('usuarios');
foreach ($filters as $tax_slug) {
$tax_obj = get_taxonomy($tax_slug);
$tax_name = $tax_obj->labels->name;
echo "<select name='$tax_slug' id='$tax_slug' class='postform'>";
echo "<option value=''>Mostrar $tax_name</option>";
generate_taxonomy_options($tax_slug,0,0);
echo "</select>";
}
}
}

function generate_taxonomy_options($tax_slug, $parent = '', $level = 0) {
$args = array('show_empty' => 1);
if(!is_null($parent)) {
$args = array('parent' => $parent);
}
$terms = get_terms($tax_slug,$args);
$tab='';
for($i=0;$i<$level;$i++){
$tab.='--';
}
foreach ($terms as $term) {
echo '<option value='. $term->slug, $_GET[$tax_slug] == $term->slug ? ' selected="selected"' : '','>' .$tab. $term->name .' (' . $term->count .')</option>';
generate_taxonomy_options($tax_slug, $term->term_id, $level+1);
}
}