Recursive Efficiency!

Hi all,

I'm trying to speed up a hierarchical tree builder with LINQ, this is what I have but it takes ages for trees that are thousands deep! Any tip on speeding this up at all?

void TreeBuilder(IEnumerable<Tree> data, int? id = null)
            {
                var items = data.Where(d => d.parentId == id).OrderBy(o => o.id);
                if (items.Any())
                {
                    foreach (var item in items)
                    {
                        teamList.Add(Tuple.Create(item.id, Convert.ToInt32(item.parentId)));
                        TreeBuilder(data, item.id);
                    }
                }
            }