Understanding TreeView in .NET Core

public IActionResult Privacy(string NODEVALUE, string NODELEVEL)
{
    if (NODELEVEL == null)
        NODELEVEL = "";
    if (NODEVALUE == null)
        NODEVALUE = "";

    List<TreeNode> liNodes = new List<TreeNode>();

    TreeNode node1 = new TreeNode
    {
        NodeText = "Text1",
        NodeValue = "Value1",
        NodeType = "PARENT",
        NodeLevel = "1"
    };
    liNodes.Add(node1);

    TreeNode node2 = new TreeNode
    {
        NodeText = "Text2",
        NodeValue = "Value2",
        NodeType = "PARENT",
        NodeLevel = "2"
    };
    liNodes.Add(node2);

    TreeNode node11 = new TreeNode
    {
        NodeText = "Text11",
        NodeValue = "Value11",
        NodeType = "PARENT",
        NodeLevel = "11"
    };
    liNodes.Add(node11);

    TreeNode node112 = new TreeNode
    {
        NodeText = "Text112",
        NodeValue = "Value112",
        NodeType = "CHILD",
        NodeLevel = "112"
    };
    liNodes.Add(node112);

    TreeNode node111 = new TreeNode
    {
        NodeText = "Text111",
        NodeValue = "Value111",
        NodeType = "CHILD",
        NodeLevel = "111"
    };
    liNodes.Add(node111);

    TreeNode node12 = new TreeNode
    {
        NodeText = "Text12",
        NodeValue = "Value12",
        NodeType = "CHILD",
        NodeLevel = "12"
    };
    liNodes.Add(node12);

    TreeNode node21 = new TreeNode
    {
        NodeText = "Text21",
        NodeValue = "Value21",
        NodeType = "CHILD",
        NodeLevel = "21"
    };
    liNodes.Add(node21);

    TreeNode node22 = new TreeNode
    {
        NodeText = "Text22",
        NodeValue = "Value22",
        NodeType = "CHILD",
        NodeLevel = "22"
    };
    liNodes.Add(node22);

    liNodes = liNodes.OrderBy(x => x.NodeLevel).ToList();

    var nodes = "";
    foreach (TreeNode node in liNodes)
    {
        nodes += node.NodeLevel.ToString() + ";";
    }

    ViewBag.NodeLevels = nodes;
    var expandnodes = splitstring(NODELEVEL);
    ViewBag.ExpandNodes = expandnodes;

    return View(liNodes);
}

Below is JavaScript

function restoreTreeState(pastnodevalues) {
    const expandnodes = pastnodevalues.split(';');
    expandnodes.forEach(clicknodes);
}

function clicknodes(item) {
    var cl = '.' + 'Class' + item;
    $(cl).click();
}

function toggleexpand(event, level, nodelevels2) {
    var nextLevel = '';
    var found = false;

    if ($(event.target).text().indexOf('-') > -1) {
        $(event.target).text($(event.target).text().replace("-", "+"));
        var lastchar = level.substring(level.length - 1);
        var nxtlevel = level.substring(0, level.length - 1);
        var nxtlevel2 = nxtlevel + (Number(lastchar) + 1);
        nextLevel = level + '1';

        for (let i = 1; i < nodelevels2.length; i++) {
            if (nodelevels2[i] >= nextLevel) {
                if (nodelevels2[i].startsWith(nxtlevel2)) {
                    break;
                }
                var cl = '.' + 'Class' + nodelevels2[i];
                $(cl).css('display', 'none');
            }
        }
    } else {
        $(event.target).text($(event.target).text().replace("+", "-"));
        nextLevel = level + 1;
        var length = nextLevel.length;
        var x = 1;

        for (let i = 1; i < nodelevels2.length; i++) {
            if (nodelevels2[i] == nextLevel) {
                if (nodelevels2[i].length != length) break;

                var cl = '.' + 'Class' + nodelevels2[i];
                if ($(cl).text().indexOf('-') > -1) {
                    $(cl).text($(cl).text().replace("-", "+"));
                }
                $(cl).css('display', 'block');
                $(cl).css('margin-left', (Number(nodelevels2[i].length) * 10).toString() + 'Px');
                x++;
                nextLevel = (level + x).toString();
            }
        }
    }
}

function SelectNode(nodevalue, nodelevel) {
    var url = window.location.toString();
    url = updateQueryStringParameter(url, "NODEVALUE", nodevalue);
    url = updateQueryStringParameter(url, "NODELEVEL", nodelevel);
    window.location = url;
}

function updateQueryStringParameter(uri, key, value) {
    var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i");
    var separator = uri.indexOf('?') !== -1 ? "&" : "?";
    
    if (uri.match(re)) {
        return uri.replace(re, '$1' + key + "=" + value + '$2');
    } else {
        return uri + separator + key + "=" + value;
    }
}

Below is model

namespace treeview.Models
{
    public class TreeNode
    {
        public string NodeText { get; set; }
        public string NodeValue { get; set; }
        public string NodeType { get; set; }
        public string NodeLevel { get; set; }
    }
}