C#

IPAddress ip = IPAddress.Parse("192.168.0.1");

IPAddress ip2 = new IPAddress( 
   IPAddress.NetworkToHostOrder(
   IPAddress.HostToNetworkOrder((int) ip.Address) + 1)
   );

public class HashTree: System.Collections.DictionaryBase
{
   char del;
   
   public HashTree()
   {
      del = (char) 0;
   }

   public HashTree(char delimter)
   {
      del = delimter;
   }

   internal int level = 0;

   private HashTree(int level, char del):this(del)
   {
      this.level = level;
   }

   public virtual HashTree this[string key]
   {
      get
      {
         string[] tokens = key.Split(del);
         HashTree outer = this;
         foreach (string keyt in tokens)
         {
            if (!outer.Dictionary.Contains(keyt))
               outer.Dictionary.Add(keyt, new HashTree(outer.level + 1, del));
            outer = outer.Dictionary[keyt] as HashTree;
         }
         return outer;
      }
   }

   public virtual System.Collections.ICollection Keys
   {
      get
      {
         return this.Dictionary.Keys;
      }
   }

   public virtual System.Collections.ICollection Values
   {
      get
      {
         return this.Dictionary.Values;
      }
   }

   private object obj;

   public object Value 
   {
      get {return obj;}
      set {obj = value;}
   }

   public string ToXml()
   {
      StringBuilder output = new StringBuilder();

      string pad = "";
      for (int i = 0; i < level; i++)
         pad += "\t";

      foreach (string key in Keys)
         output.AppendFormat("{2}<{0}>\n{1}{2}</{0}>\n",
            key, (this[key].Count > 0 ? this[key].ToXml() : (pad + "\t" + this[key].Value + "\n")), pad);
      return output.ToString();
   }
}

HashTree tree = new HashTree('.');

foreach(....)
{
  tree
    ["rootlevel"]
      ["nextlevel"]
        ["anotherlevel"]
          .Value = "somevalue"; //dont you love funky usage?
  //or the same thing
  tree["rootlevel.nextlevel.anotherlevel"].Value = "somevalue";
}

string xml = tree.ToXml();