JSFiddle - React, Tailwind, and code Playground

HTML

<div id="demo_1">
    <ul class="ltr">
        <li id="phtml_1" class="open"><a href="#"><ins>&nbsp;</ins>Root node 1</a>
            <ul>
                <li class="leaf" id="phtml_2"><a href="#"><ins>&nbsp;</ins>Child node 1</a></li>
                <li class="last leaf" id="phtml_3"><a href="#"><ins>&nbsp;</ins>Child node 2</a></li>
            </ul>
        </li>
        <li id="phtml_5" class="file last leaf"><a href="#"><ins>&nbsp;</ins>Root node 2</a></li>
    </ul>
</div>
<div id="show_tree"></div>

JavaScript

var treeInnerHTML = $("#demo_1").html();
$.ajax({
    type: 'POST',
    url: "/ajax_html_echo/",
    data: {
        html: treeInnerHTML
    },
    success: function (data) {
        $("#show_tree").html(data);
    },
    error: function (req, status, error) {}
});