using System;
using System.Xml.Linq;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

public class JsonToXmlConverter
{
    public static XDocument ConvertJsonToXml(string json)
    {
        var doc = new XDocument();
        var root = new XElement("root");
        var obj = JObject.Parse(json);
        FillXElement(root, obj);
        doc.Add(root);
        return doc;
    }

    private static void FillXElement(XElement element, JToken token)
    {
        foreach (var child in token.Children())
        {
            if (child is JProperty prop)
            {
                if (prop.Value is JValue || !(prop.Value.HasValues))
                {
                    var childElement = new XElement(prop.Name);
                    childElement.Value = prop.Value.ToString();
                    element.Add(childElement);
                }
                else
                {
                    var childElement = new XElement(prop.Name);
                    FillXElement(childElement, prop.Value);
                    element.Add(childElement);
                }
            }
            else if (child is JValue val)
            {
                element.Value = val.ToString();
            }
        }
    }
}

string json = @"{ 'name': 'Alice', 'age': 30, 'address': { 'city': 'Beijing', 'zip': '100000' } }";
var xmlDoc = JsonToXmlConverter.ConvertJsonToXml(json);
Console.WriteLine(xmlDoc.ToString());

<root>
  <name>Alice</name>
  <age>30</age>
  <address>
    <city>Beijing</city>
    <zip>100000</zip>
  </address>
</root>

"items": [ "apple", "banana" ]

<items>
  <item>apple</item>
  <item>banana</item>
</items>