Why is there no Tree<T> class in .NET?

The base class library in .NET has some excellent data structures for collections (List, Queue, Stack, Dictionary), but oddly enough it does not contain any data structures for binary trees. This is a terribly useful structure for certain algorithms, such as those that take advantage of different traversal paths. I'm looking for a correctly written, free implementation.

Am I simply blind, and not finding it... is it buried somewhere in the BCL? If not, can someone recommend a free or open-source C#/.NET library for binary trees? Preferably one that employs generics.

EDIT: To clarify what I'm looking for. I'm not interested in ordered dictionary collections that internally use a tree. I'm actually interested in a binary tree - one that exposes its structure so that you can do things like extract subtrees, or perform post-fix traversal on the nodes. Ideally such a class could be extended to provide the behaviors of specialized trees (ie. Red/Black, AVL, Balanced, etc).

Solution 1:

You could define your own:

public class MyTree<K, V> : Dictionary<K, MyTree<K, V>>
{
    public V Value { get; set; }
}

Or unkeyed:

public class MyTree<V> : HashSet<MyTree<V>>
{
    public V Value { get; set; }
}

Solution 2:

What would you want from such an implementation?

Binary tree? Red-black? Radix tree? B-tree? R-tree? R*-tree?

A tree is more a pattern than a data structure, and they tend to be used where performance matters (so implementation details probably matter too). If the BCL included some kind of a tree class, you'd only have to roll your own anyway

Solution 3:

You're right, there's nothing in the BCL. I suspect this is because the choice of whether to use a tree is typically an implementation detail and is otherwise an unconventional way to access data. That is, you don't say, "binary-search-for element #37"; instead, you say, "get me element #37".

But have you taken a look at C5? It's super-handy and they have several tree implementations (1, 2, 3).