function parse_query( $query ) {
    global $pagenow;
    // Change query based on post_parent
    $parent_filter = $_GET['parent'];
    if ( is_admin() && $pagenow == 'edit.php' && ! empty( $parent_filter ) ) {
        $query->query_vars['post_parent'] = (int) $parent_filter;
    }
}

public static function restrict_manage_posts() {

    if ( isset( $_GET['post_type'] ) && $_GET['post_type'] == 'episode' ) {
        $args     = [
            'post_type'   => 'podcast',
            'numberposts' => - 1,
        ];
        $podcasts = get_posts( $args );

        $select = '<select name="parent"><option value="">Podcast (' . count( $podcasts ) . ')</option>';
        foreach ( $podcasts as $podcast ) {
            $selected = ( isset( $_GET['parent'] ) && (int) $_GET['parent'] > 0 ) ? 'selected="selected"' : '';
            $select   .= '<option value="' . $podcast->ID . '" ' . $selected . '>' . $podcast->post_title . '</option>';
        }
        $select .= '</select>';
        echo $select;
    } else {
        return;
    }
}