How I add dropdown list in existing navbar drop down list.. (In other words how I make a nested dropdown list? )

<pre> <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
        <div class="container-fluid">
            <img src="upsida-logo-name.png" alt="png" class="logo">
            <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
                
              </button>
            <div class="collapse navbar-collapse" id="navbarSupportedContent">
                <ul class="navbar-nav me-auto mb-2 mb-lg-0">
                    <li class="nav-item">
                        <a class="nav-link active" aria-current="page" href="#">Home</a>
                    </li>
                    <li class="nav-item dropdown">
                        <a class="nav-link dropdown-toggle" id="navbarDropdown" role="button"
                            data-bs-toggle="dropdown" aria-expanded="false">
                            Department
                        </a>
                        <ul  class="dropdown-menu" aria-labelledby="navbarDropdown">
                            <li><a class="dropdown-item" href="#">About Us</a></li>
                            <li><a class="dropdown-item" href="#">Contact Us</a></li>
                            <li><a class="dropdown-item" href="#">Office orders</a></li>
                        </ul>
                    </li>