Nav bar menu drop down bootstrap

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bootstrap

Below is my nav bar menu code.

 <div class="navbar-collapse collapse" id="navbarCustom">
                <ul class="navbar-nav mr-auto">
                    <li class="nav-item dropdown">
                        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown1" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Menu1</a>
                        <div class="dropdown-menu border-0" aria-labelledby="navbarDropdown1">
                            <a class="dropdown-item" href="#">Menu1</a>
                            <div class="dropdown-divider"></div>
                            <a class="dropdown-item" href="#">Menu2</a>
                            <div class="dropdown-divider"></div>
                            <a class="dropdown-item" href="#">Menu3</a>
                            <div class="dropdown-divider"></div>
                            <a class="dropdown-item" href="#">Menu4</a>
                            <div class="dropdown-divider"></div>
                            <a class="dropdown-item" href="#">Menu5</a>
                        </div>
                    </li>
                </ul>
</div>

I need to create submenu to 'Menu4'.

What I have tried:

I was not able to find submenu class. Am using Bootstrap v4.5