JSFiddle - React, Tailwind, and code Playground

HTML

<ol class="treeRoot"><li class="is-parent is-collapsed">
        <a>Lorem ipsum dolor sit amet</a>
            <ol><li>
                    <a>consetetur sadipscing elitr</a>
                </li><li class="is-parent is-collapsed">
                    <a>sed diam nonumy eirmod tempor invidunt ut</a>
                    <ol><li class="is-parent is-collapsed">
                            <a>labore et dolore magna aliquyam erat, sed diam voluptua</a>
                    <ol><li>
                            <a>At vero eos et accusam et justo duo dolores</a>
                        </li><li class="is-parent is-collapsed is-last-child">
                            <a>et ea rebum. Stet clita kasd gubergren</a>
                    <ol><li>
                            <a>no sea takimata sanctus est</a>
                        </li><li class="is-last-child">
                            <a>Lorem ipsum dolor sit amet</a>
                        </li></ol>
                        </li></ol>
                        </li><li class="is-last-child">
                            <a>Lorem ipsum dolor sit amet, consetetur sadipscing elitr</a>
                        </li></ol>
                </li><li>
                    <a>sed diam nonumy eirmod tempor</a>
                </li><li>
                    <a>A 4 Heimatsparkassengrundsätze</a>
                </li><li>
                    <a>invidunt ut labore et dolore magna aliquyam erat</a>
                </li><li>
                    <a>sed diam voluptua</a>
                </li><li class="is-last-child">
                    <a>At vero eos et accusam et justo</a>
                </li></ol>
        </li><li class="is-parent is-collapsed">
            <a>duo dolores et ea rebum</a>
            <ol><li class="is-last-child">
                <a>Stet clita kasd gubergren</a>
                </li></ol>
        </li><li class="is-last-child">
            <a>no sea takimata sanctus est Lorem ipsum dolor sit amet</a>
        </li></ol>

CSS

.treeRoot ol,
.treeRoot {
    padding: 0;
    margin: 0;
    list-style: none;
    line-height: 16px;
    background-color: #a6c2bb;
}
.treeRoot {
    border: 1px solid #a6c2bb;
}
.treeRoot ol {
    background: #f1f1f1;
    display: none;
    padding-bottom: 15px;
}
.treeRoot li {
    position: relative;
    -webkit-transition: background .2s ease;
    -moz-transition: background .2s ease;
    -o-transition: background .2s ease;
    transition: background .2s ease;
}
.treeRoot li.is-expanded > a,
.treeRoot a:hover {
    font-weight: bold;
}
.treeRoot a:hover {
    color: #385b50;
}
.treeRoot li:hover {
    background-color: #ccc;
}
.treeRoot li.is-expanded {
    background: #fff;
}
.treeRoot li > a {
    padding: 3px 0;
    cursor: pointer;
    position: relative;
    display: block;
    font-weight: normal;
    color: #000;
    text-decoration: none;
}
.treeRoot li.is-parent > a {
    background: url(img/Navigation/minus.png) no-repeat 0 7px;
    padding-left: 15px;
}
.treeRoot li.is-parent.is-collapsed > a {
    background-image: url(img/Navigation/plus.png);
}
.treeRoot li.is-parent.is-collapsed > a:after {
    display: none;
}
.treeRoot li.is-parent > a:after {
    content: "";
    position: absolute;
    top: 20px;
    bottom: -11px;
    left: 4px;
    border-left: 1px dotted #000;
}
.treeRoot li li:after {
    content: "";
    position: absolute;
    top: 11px;
    bottom: -10px;
    width: 16px;
    border-left: 1px dotted #000;
    border-top: 1px dotted #000;
}
.treeRoot li li.is-last-child:after {
    bottom: auto;
    height: 0;
}
.treeRoot > li.is-parent > a:after {
    left: 14px;
}
.treeRoot > li {
    border: 1px solid #fff;
    background: #f1f1f1;
    margin-top: 1px;
}
.treeRoot > li:first-child {
    margin-top: 0;
}
.treeRoot > li > a {
    padding: 5px 10px;
    border-top: 0;
    display: block;
    margin: 0;
}
.treeRoot > li.is-parent > a {
    background-position: 10px 8px;
    padding-left: 25px;
}
.treeRoot li li > a {
   ...

JavaScript

$('a').on('click', function (e) {
    $(this).parent().toggleClass('is-collapsed').toggleClass('is-expanded');
    $(this).next().slideToggle();
});