Saving new children/subchildren in XML

I've been following this page, and I've gotten stuck at the saving section of the code. I am trying to get every gameobject tagged tile, and save it's x, y, and tile type values.

I can get the variables from the objects. However, I cannot figure out how to save the XML document. I want to create a section for each object, and have subchildren data where it lists the x, y, and tile types.

     <?xml version="1.0" encoding="UTF-8"?>
     <ItemCollection>
       <Items>
         <Item index="0">
           <XPos>0</XPos>
           <YPos>0</YPos>
           <TileType>0</TileType>
         </Item>
         <Item index="1">
           <XPos>2</XPos>
           <YPos>5</YPos>
           <TileType>3</TileType>
         </Item>
       </Items>
     </ItemCollection>

Above is an example of what XML document I want to generate.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using System.Xml.Serialization;
 using System.IO;
 
 [XmlRoot("ItemCollection")]
 public class ItemContainer {
 
     [XmlArray("Items")]
     [XmlArrayItem("Item")]
     public List<Item> items = new List<Item>();
 
     public static ItemContainer Load(string path)
     {
         TextAsset _xml = Resources.Load<TextAsset>(path);
 
         XmlSerializer serializer = new XmlSerializer(typeof(ItemContainer));
 
         StringReader reader = new StringReader(_xml.text);
 
         ItemContainer items = serializer.Deserialize(reader) as ItemContainer;
 
         reader.Close();
 
         return items;
     }
 }

That is the code I am using for loading in data. How would I go about saving new data based upon variables, and resetting the XML document at each save (so it can reload all of the XML data)?