By adding a few lines of additional CSS you can add extra levels of submenu to your dropdown. You can apply this to the dropdown in a simple button or within the navbar.
To learn more about dropdowns read Dropdown Docs.
An example of a nested dropdown with a simple button.
HTML
<div class="dropdown">
<button
class="btn btn-primary dropdown-toggle"
type="button"
id="dropdownMenuButton"
data-mdb-toggle="dropdown"
aria-expanded="false"
>
Dropdown button
</button>
<ul class="dropdown-menu" aria-labelledby="dropdownMenuButton">
<li><a class="dropdown-item" href="#">Action</a></li>
<li>
<a class="dropdown-item" href="#">Another action</a>
</li>
<li>
<a class="dropdown-item" href="#">
Submenu »
</a>
<ul class="dropdown-menu dropdown-submenu">
<li>
<a class="dropdown-item" href="#">Submenu item 1</a>
</li>
<li>
<a class="dropdown-item" href="#">Submenu item 2</a>
</li>
<li>
<a class="dropdown-item" href="#">Submenu item 3 » </a>
<ul class="dropdown-menu dropdown-submenu">
<li>
<a class="dropdown-item" href="#">Multi level 1</a>
</li>
<li>
<a class="dropdown-item" href="#">Multi level 2</a>
</li>
</ul>
</li>
<li>
<a class="dropdown-item" href="#">Submenu item 4</a>
</li>
<li>
<a class="dropdown-item" href="#">Submenu item 5</a>
</li>
</ul>
</li>
</ul>
</div>
CSS
.dropdown-menu li {
position: relative;
}
.dropdown-menu .dropdown-submenu {
display: none;
position: absolute;
left: 100%;
top: -7px;
}
.dropdown-menu .dropdown-submenu-left {
right: 100%;
left: auto;
}
.dropdown-menu > li:hover > .dropdown-submenu {
display: block;
}