gistfile1.cs

public class TreeNode<TName, TTag> {
   internal TreeNodeCollection<TName, TTag> nodes;
   
   public TreeNode(TName name) {
       Name = name;
   }

   public TName Name { get; set; }

   public TTag Tag { get; set; }
   
   public TreeNode<TName, TTag> Parent { get; set; }

   public TreeNodeCollection<TName, TTag> Nodes {
       get {
           if (this.nodes == null) {
               this.nodes = new TreeNodeCollection<TName, TTag>(this);
           }

           return this.nodes;
       }
   }
}

public class TreeNodeCollection<TName, TTag> : IEnumerable<TreeNode<TName, TTag>> {
   private TreeNode<TName, TTag> m_parent;
   
   private List<TreeNode<TName, TTag>> m_innerList = new List<TreeNode<TName, TTag>>();

   internal TreeNodeCollection(TreeNode<TName, TTag> parent) {
       m_parent = parent;
   }

   public TreeNode<TName, TTag> this[int index] {
       get {
           if (index < 0 || index >= m_innerList.Count) throw new ArgumentOutOfRangeException("index");
           
		   return m_innerList[index];
       }            
   }
   
   public int Count {
       get { return m_innerList.Count; }
   }
   
    public void Add(TreeNode<TName, TTag> node) {
		node.Parent = m_parent;
		m_innerList.Add(node);
    }

   public void Remove(TreeNode<TName, TTag> node) {
       m_innerList.Remove(node);
   }
   
    public TreeNode<TName, TTag> Parent {
       get {
           return m_parent;
       }
   }
   
   public IEnumerator<TreeNode<TName, TTag>> GetEnumerator()
   {
       return m_innerList.GetEnumerator();
   }

   System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
   {
       return GetEnumerator();
   }
}

Generic tree implementation inspired on WinForms's TreeView TreeNode/ TreeNodeCollection

TName is generic type of all nodes name (usually string)
TTag is generic type of all nodes tags (usually struct/own class definition )

This tag can be attached both on leaf and non-leaf nodes nodes