MongoServer server = MongoServer.Create(ConnectionString);
            MongoDatabase myCompany = server.GetDatabase("MyCompany");
            MongoCollection<BsonDocument> departments = myCompany.GetCollection<BsonDocument>("Departments");
            BsonDocument deptartment = new BsonDocument {
                        { "DepartmentName", departmentName },
                        { "HeadOfDepartmentId", headOfDepartmentId }
                        };
            departments.DropAllIndexes();

            var keys = IndexKeys.Ascending("ts");
            var options = IndexOptions.SetTimeToLive(TimeSpan.FromSeconds(5));
            departments.EnsureIndex(keys, options);
            departments.Insert(deptartment);