Stashbox by Peter Csajtai

ImmutableTree<TValue>

sealed class ImmutableTree<TValue>

public static readonly ImmutableTree<TValue> Empty

public readonly bool IsEmpty

public ImmutableTree<TValue> AddOrUpdate(int key, TValue value, Func<TValue, TValue, TValue> updateDelegate = null)

public TValue GetOrDefault(int key)