Gets all child items

gistfile1.cs

private static IEnumerable<CollectionMemberCached> Descendants(CollectionMemberCached root)
        {
            var nodes = new Stack<CollectionMemberCached>(new[] { root });
            while (nodes.Any())
            {
                CollectionMemberCached node = nodes.Pop();
                yield return node;
                foreach (var n in node.Members)
                    nodes.Push(n);
            }
        }

//usage 
var collecationMembers =
                allCollections.SelectMany(q => q.Members)
                    .SelectMany(Descendants)
                    .Where(q => q.Type == CollectionMemberType.User && !q.Excluded)
                    .ToList();

/* 
 public class CollectionMemberCached
    {
        public CollectionMemberCached()
        {
            Members = new List<CollectionMemberCached>();
        }

        public Guid ObjectGuid { get; set; }
        public string Name { get; set; }
        public string Email { get; set; }
        public bool Excluded { get; set; }
        public CollectionMemberType Type { get; set; }
        public List<CollectionMemberCached> Members { get; set; }

*/