public IEnumerable <int> Select(IEnumerable <int> sequence, Func <int, bool> call_back_fun) { if (sequence == null) { throw new ArgumentException("sequence cann't be null"); } BPlusTree TempTree = new BPlusTree(); foreach (int elem in sequence) { if (call_back_fun(elem)) { TempTree.insert(elem); } } return(TempTree.Get_all_data(1000)); }