如何根据起始文本从相同级别的元素生成嵌套列表

请帮助制作基于列表项（相同级别）的嵌套列表，但具有不同的标签文本，这将开始每个列表项的文本。我已经完成了一些正则表达式替换以满足嵌套。我假设我的代码不符合分组|嵌套的要求。请提出建议。

IN.xnl：

<article>
<p>The Simple list sample</p>
<list-item>1. First</list-item>
<list-item>2. Second</list-item>
<list-item>3. Third</list-item>
<p>The Nested list sample</p>
<list-item>1. FirstLevel First Text</list-item>
<list-item>1.1 SecondLevel First Text</list-item>
<list-item>1.1.1 ThirdLevel First Text</list-item>
<list-item>1.1.2 ThirdLevel Second Text</list-item>
<list-item>1.2 SecondLevel Second Text</list-item>
<list-item>2. FirstLevel Second Text</list-item>
<list-item>2.1 SecondLevel First Text</list-item>
<list-item>2.2 SecondLevel Second Text</list-item>
<list-item>3. FirstLevel Third Text</list-item>
<list-item>4. FirstLevel Fourth Text</list-item>
</article>

C#（试用代码）：

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text.RegularExpressions;
using System.Xml;
using System.Xml.Linq;
using System.Xml.XPath;
using System.Linq;
using System.Linq.Expressions;

namespace ListNesting1
{
    class Program
    {
        static void Main(string[] args)
        {
            XmlDocument XMLDoc1 = new XmlDocument();
            XmlNodeList NDL1, NDL2, NDL3, NDL4, NDL5, NDL6, NDL7;
            XmlElement XEle1;
           
            String S1, S2, S3 = "", S4, StrFinal, StrEle1;
            StreamReader SR1;
            StreamWriter SW1;

            try
            {
                SR1 = new StreamReader(args[0]);
                S1 = SR1.ReadToEnd();
                SR1.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
                return;
            }

            XMLDoc1.LoadXml(S1);

            NDL1 = XMLDoc1.SelectNodes("//list-item");

            for(int i=0; i<NDL1.Count; i++)
            {
                if (Regex.IsMatch(NDL1[i].InnerText, @"^[0-9]\. "))
                    {
                    StrEle1 = "List1";
                }
                
                else if (Regex.IsMatch(NDL1[i].InnerText, @"^[0-9]\.[0-9] "))
                {
                    StrEle1 = "List2";
                }
                else if (Regex.IsMatch(NDL1[i].InnerText, @"^[0-9]\.[0-9]\.[0-9] "))
                {
                    StrEle1 = "List3";
                }
                else
                {
                    StrEle1 = "List4";
                }
                XEle1 = XMLDoc1.CreateElement(StrEle1);
                S2 = NDL1[i].OuterXml;
                XEle1.InnerXml = S2;
                
                NDL1[i].ParentNode.InsertAfter(XEle1, NDL1[i]);
                NDL1[i].ParentNode.RemoveChild(NDL1[i]);
            }

            StrFinal = XMLDoc1.OuterXml;
            StrFinal = StrFinal.Replace("</List1><List1>", "");
            StrFinal = StrFinal.Replace("</List2><List2>", "");
            StrFinal = StrFinal.Replace("</List3><List3>", "");
            StrFinal = StrFinal.Replace("</List4><List4>", "");

            StrFinal = StrFinal.Replace("</list-item></List1><List2>", "<List2>");
            StrFinal = StrFinal.Replace("</list-item></List2><List3>", "<List3>");
            StrFinal = StrFinal.Replace("</list-item></List3><List4>", "<List4>");

            StrFinal = StrFinal.Replace("</List2><List1>", "</List2></list-item>");
            StrFinal = StrFinal.Replace("</List3><List2>", "</List3></list-item>");
            StrFinal = StrFinal.Replace("</List4><List3>", "</List4></list-item>");

            StrFinal = StrFinal.Replace("><", ">\n<");

            SW1 = new StreamWriter(args[1]);
            SW1.Write(StrFinal);
            SW1.Close();
        }
    }
}

所需XML:

<article>
<p>The Simple list sample</p>
<List1>
<list-item>1. First</list-item>
<list-item>2. Second</list-item>
<list-item>3. Third</list-item>
</List1>
<p>The Nested list sample</p>
<List1>
<list-item>1. FirstLevel First Text
    <List2>
        <list-item>1.1 SecondLevel First Text
            <List3>
            <list-item>1.1.1 ThirdLevel First Text</list-item>
            <list-item>1.1.2 ThirdLevel Second Text</list-item>
            </List3>
        </list-item>
        <list-item>1.2 SecondLevel Second Text</list-item>
    </List2>
</list-item>
<list-item>2. FirstLevel Second Text
    <List2>
    <list-item>2.1 SecondLevel First Text</list-item>
    <list-item>2.2 SecondLevel Second Text</list-item>
    </List2>
</list-item>
<list-item>3. FirstLevel Third Text</list-item>
<list-item>4. FirstLevel Fourth Text</list-item>
</List1>
</article>