Bootstrap 4 dropdown submenu dropup variation - html

Question

I am using Bootstrap 4 button dropdown. I want the dropdown menu to dropup. Using the dropup class as told here How to get a Bootstrap dropdown submenu to 'dropup', I somehow still cannot get the sub menu (Days and Hours in my code) to drop up.
HTML
<div class="dropup">
<button style="width:220px" class="btn btn-secondary dropdown-toggle ml-auto" type="button" id="dropdownMenu3" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Period</button>
<ul class="dropdown-menu dropup multi-level" role="menu" aria-labelledby="dLabel" id="option2">
<li class="dropdown-submenu others">Days
<ul class="dropdown-menu bottom-up" id="days">
<li class="dropdown-item option">1</li>
<li class="dropdown-item option">2</li>
<li class="dropdown-item option">3</li>
<li class="dropdown-item option">4</li>
</ul>
</li>
<li class="dropdown-submenu others">Hours
<ul class="dropdown-menu" id="hours">
<li class="dropdown-item option">1</li>
<li class="dropdown-item option">2</li>
<li class="dropdown-item option">3</li>
<li class="dropdown-item option">4</li>
</ul>
</li>
</ul>
</div>
CSS
<style>
.dropdown-submenu {
position: relative;
}
.dropdown-submenu>.dropdown-menu {
top: 0;
left: 100%;
margin-top: -6px;
margin-left: -1px;
-webkit-border-radius: 0 6px 6px 6px;
-moz-border-radius: 0 6px 6px;
border-radius: 0 6px 6px 6px;
}
.dropdown-submenu:hover>.dropdown-menu {
display: block;
}
.dropdown-submenu.pull-left {
float: none;
}
.dropdown-submenu.pull-left>.dropdown-menu {
left: -100%;
margin-left: 10px;
-webkit-border-radius: 6px 0 6px 6px;
-moz-border-radius: 6px 0 6px 6px;
border-radius: 6px 0 6px 6px;
}
</style>
Thank you in advance for the help! :)