nav-item dropdown

  <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
    <a class="navbar-brand" href="#">ブランド</a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav"
      aria-controls="navbarNav" aria-expanded="false" aria-label="ナビゲーション切替">
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarNav">
      <ul class="navbar-nav">
        <li class="nav-item dropdown">
          <!-- dropdown-toggleを使う -->
          <a class="nav-link dropdown-toggle" href="#" id="navbarDropdownMenu" data-toggle="dropdown"
            aria-haspopup="true" aria-expanded="false">
            ドロップダウンメニュー
          </a>
          <div class="dropdown-menu" aria-labelledby="navbarDropdownMenu">
            <a class="dropdown-item" href="#">サブメニュー1</a>
            <a class="dropdown-item" href="#">サブメニュー2</a>
            <a class="dropdown-item" href="#">サブメニュー3</a>
          </div>
        </li>
        <li class="nav-item active"><a class="nav-link" href="#">メニュー1</a></li>
        <li class="nav-item active"><a class="nav-link" href="#">メニュー2</a></li>
        <li class="nav-item"><a class="nav-link" href="#">メニュー3</a></li>
      </ul>
    </div>
  </nav>

  <ul class="nav nav-pills">
    <li class="nav-item"><a class="nav-link active" href="#">アクティブ</a></li>
    <li class="nav-item dropdown">
      <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true"
        aria-expanded="false">ドロップダウン</a>
      <div class="dropdown-menu">
        <a class="dropdown-item" href="#">リンク1</a>
        <a class="dropdown-item" href="#">リンク2</a>
        <a class="dropdown-item" href="#">リンク3</a>
        <div class="dropdown-divider"></div>
        <a class="dropdown-item" href="#">その他リンク</a>
      </div>
    </li>
    <li class="nav-item"><a class="nav-link" href="#">リンク</a></li>
    <li class="nav-item"><a class="nav-link disabled" href="#">無効</a></li>
  </ul>

  <ul class="nav nav-tabs">
    <li class="nav-item"><a class="nav-link active" href="#">アクティブ</a></li>
    <li class="nav-item dropdown">
      <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true"
        aria-expanded="false">ドロップダウン</a>
      <div class="dropdown-menu">
        <a class="dropdown-item" href="#">リンク1</a>
        <a class="dropdown-item" href="#">リンク2</a>
        <a class="dropdown-item" href="#">リンク3</a>
        <div class="dropdown-divider"></div>
        <a class="dropdown-item" href="#">その他リンク</a>
      </div>
    </li>
    <li class="nav-item"><a class="nav-link" href="#">リンク</a></li>
    <li class="nav-item"><a class="nav-link disabled" href="#">無効</a></li>
  </ul>