_wp_ajax_add_hierarchical_term

function _wp_ajax_add_hierarchical_term() {
	$action   = $_POST['action'];
	$taxonomy = get_taxonomy( substr( $action, 4 ) );
	check_ajax_referer( $action, '_ajax_nonce-add-' . $taxonomy->name );

	if ( ! current_user_can( $taxonomy->cap->edit_terms ) ) {
		wp_die( -1 );
	}

	$names  = explode( ',', $_POST[ 'new' . $taxonomy->name ] );
	$parent = isset( $_POST[ 'new' . $taxonomy->name . '_parent' ] ) ? (int) $_POST[ 'new' . $taxonomy->name . '_parent' ] : 0;

	if ( 0 > $parent ) {
		$parent = 0;
	}

	if ( 'category' === $taxonomy->name ) {
		$post_category = isset( $_POST['post_category'] ) ? (array) $_POST['post_category'] : array();
	} else {
		$post_category = ( isset( $_POST['tax_input'] ) && isset( $_POST['tax_input'][ $taxonomy->name ] ) ) ? (array) $_POST['tax_input'][ $taxonomy->name ] : array();
	}

	$checked_categories = array_map( 'absint', (array) $post_category );
	$popular_ids        = wp_popular_terms_checklist( $taxonomy->name, 0, 10, false );

	foreach ( $names as $cat_name ) {
		$cat_name          = trim( $cat_name );
		$category_nicename = sanitize_title( $cat_name );

		if ( '' === $category_nicename ) {
			continue;
		}

		$cat_id = wp_insert_term( $cat_name, $taxonomy->name, array( 'parent' => $parent ) );

		if ( ! $cat_id || is_wp_error( $cat_id ) ) {
			continue;
		} else {
			$cat_id = $cat_id['term_id'];
		}

		$checked_categories[] = $cat_id;

		if ( $parent ) { // Do these all at once in a second.
			continue;
		}

		ob_start();

		wp_terms_checklist(
			0,
			array(
				'taxonomy'             => $taxonomy->name,
				'descendants_and_self' => $cat_id,
				'selected_cats'        => $checked_categories,
				'popular_cats'         => $popular_ids,
			)
		);

		$data = ob_get_clean();

		$add = array(
			'what'     => $taxonomy->name,
			'id'       => $cat_id,
			'data'     => str_replace( array( "\n", "\t" ), '', $data ),
			'position' => -1,
		);
	}

	if ( $parent ) { // Foncy - replace the parent and all its children.
		$parent  = get_term( $parent, $taxonomy->name );
		$term_id = $parent->term_id;

		while ( $parent->parent ) { // Get the top parent.
			$parent = get_term( $parent->parent, $taxonomy->name );
			if ( is_wp_error( $parent ) ) {
				break;
			}
			$term_id = $parent->term_id;
		}

		ob_start();

		wp_terms_checklist(
			0,
			array(
				'taxonomy'             => $taxonomy->name,
				'descendants_and_self' => $term_id,
				'selected_cats'        => $checked_categories,
				'popular_cats'         => $popular_ids,
			)
		);

		$data = ob_get_clean();

		$add = array(
			'what'     => $taxonomy->name,
			'id'       => $term_id,
			'data'     => str_replace( array( "\n", "\t" ), '', $data ),
			'position' => -1,
		);
	}

	ob_start();

	wp_dropdown_categories(
		array(
			'taxonomy'         => $taxonomy->name,
			'hide_empty'       => 0,
			'name'             => 'new' . $taxonomy->name . '_parent',
			'orderby'          => 'name',
			'hierarchical'     => 1,
			'show_option_none' => '— ' . $taxonomy->labels->parent_item . ' —',
		)
	);

	$sup = ob_get_clean();

	$add['supplemental'] = array( 'newcat_parent' => $sup );

	$x = new WP_Ajax_Response( $add );
	$x->send();
}