If you ever find yourself in need of a data structure that is not present in the .NET Framework you should check out these free collections that contain C# implementations of trees, heaps and many other data structures:
- The C5 Generic Collection Library for C# and CLI is a library of generic collection classes for C# and other CLI languages (.Net 2.0 and later, and Mono 1.2 and later). There is a freely downloadable book about C5.
- Wintellect’s Power Collections for .NET: The goal of the project is to provide generic collection classes that are not available in the .NET framework. Some of the collections included are the Deque, MultiDictionary, Bag, OrderedBag, OrderedDictionary, Set, OrderedSet, and OrderedMultiDictionary.