Sub tab in sub tab sidenav

This is the code but it doesnt work. I want to have a subtab in a subtab but the subtab doesnt open as I want   <li><a class="collapsible-header waves-effect arrow-r"><i class="fa fa-chevron-right"></i> Sprint 1<i class="fa fa-angle-down rotate-icon"></i></a> <div class="collapsible-body"> <ul class="list-unstyled"> <li><a class="collapsible-header waves-effect arrow-r"><i class="fa fa-chevron-right"></i> Sprint 0<i class="fa fa-angle-down rotate-icon"></i></a> <div class="collapsible-body"> <ul class="list-unstyled"> <li><a href="../../Sprint_1/Variables/thisisme.php" class="waves-effect">Thisisme</a> </li> <li><a href="../../Sprint_1/Variables/quotes.php" class="waves-effect">Quotes</a> </li> <li><a href="../../Sprint_1/Variables/scope.php" class="waves-effect">Scope</a> </li> </ul> </div> </li> <li><a href="../../Sprint_1/Operators/compare.php" class="waves-effect">Compare</a> </li> <li><a href="../../Sprint_1/Operators/operators.php" class="waves-effect">Operators</a> </ul> </div> </li>

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