[c#]
private NodeBase AddWord(FlyGrid flyGrid, Word word)
{
  //search for node associated with headword
  NodeBase node = SearchHeadWord(flyGrid.Rows.Items, word);
  //if node not found - create and add node with headword
  if (node == null)
    node = AddHeadWord(flyGrid.Rows.Items, word);
  //add word to the headword node
  return AddWord(node, word);  
}

private NodeBase SearchHeadWord(NodeCollection nodes, Word word)
{
  for(int i=0; i < nodes.Count; i++)
  {
    NodeBase node = nodes[i];//get node
    //try to extract HeadWord instance from node.Value
    HeadWord hword = node.Value as HeadWord;
    //if associated value is Headword - compare with word.Headword
    if (hword == word.Headword)
      return node;
    //you can scan node's children. if it is necessary
    if (node.HasChildren and node.Items != null)
    {
      node = SearchHeadWord(node.Items, word);
      if (node != null) return node;
    }
  }
  return null;
}
private NodeBase AddHeadWord(NodeCollection nodes, Word word)
{
  //create node
  Node node = new Node(word.HeadWord);
  //add node to the nodes collection
  nodes.Add(node);
  //return created node
   return node;
}
private NodeBase AddWord(NodeBase node, Word word)
{
  //create node
  Node node = new Node(word);
  //add node to the nodes collection
  node.Items.Add(node);
  return node;
}

[c#]
private static Hashtable headwords = new Hashtable();
private void RegisterHeadword(Headword hword, NodeBase node)
{
  headwords[hword] = node;  
}
private NodeBase GetNode(Headword hword)
{
  return headwords[hword] as NodeBase;
}

[c#]
private void RegisterHeadword(Headword hword, NodeBase node)
{
  hword.Node = node;
}

private NodeBase GetNode(Headword hword)
{
  return hword.Node;
}