ImmutableTree<TKey, TValue>
public ImmutableTree<TKey, TValue> AddOrUpdate(TKey key, TValue value, bool byRef, Func<TValue, TValue, TValue> updateDelegate = null)
public ImmutableTree<TKey, TValue> AddOrUpdate(TKey key, TValue value, bool byRef, bool forceUpdate)
public ImmutableTree<TKey, TValue> UpdateIfExists(TKey key, bool byRef, Func<TValue, TValue> updateDelegate)