To add menu items add to class Plugin

public function addToMainNavigation()
{
    return [
        '{tab_name}' => [
            '{name}' => [
                'label'       => {label},
                'url'         => {url},
                'permissions' => [{permission}, ...],
                'icon'        => {icon},
                'order'       => {order},
                //'first'       => true,
                'subMenu'     => [
                    '{tab_name}' => [
                        '{name}' => [
                            'label'       => {label},
                            'url'         => {url},
                            'permissions' => [{permission}, ...],
                            'icon'        => {icon},
                            'order'       => {order},
                        ],
                        ...
                    ],
                ...
            ],
            ...
        ],
        ...
    ];
}

Default tab name is {default_name}

For change default tab name, in Plugin.php file, declare the constant DEFAULT_MENU_NAME

If the first element is specified, it will immediately open when you click on the menu. If not, the menu or submenu page will be opened.