WordPress generate_rewrite_rules without specific slug

Question

Goal : I need to generate custom URL on WordPress to convert the slug into variable. Anything after slash will be considered as fruit's name.

For example, to produce banana, I need to go to website.com/u/banana

What I expected : website.com/banana

Problem : I need to remove that '/u/' part from the URL and prevent any possible conflict with other standard pages slug.

My code :

add_filter( 'generate_rewrite_rules', function ( $wp_rewrite ){
    $wp_rewrite->rules = array_merge(
        ['u/([^/]*)' => 'index.php?fruit=$matches[1]'],
        $wp_rewrite->rules
    );
} );

add_filter( 'query_vars', function( $query_vars ){ 
    $query_vars[] = 'fruit';
    return $query_vars;
} );

add_filter( 'home_template', 'wpa3396_page_template' );
function wpa3396_page_template( $page_template )
{
    if ( get_query_var( 'fruit' ) ) :
      $page_template = plugin_dir_path( __FILE__ ) . 'templates/fruitcase.php';
      return $page_template;
    endif;
}