var newtable = new table()
                            {
                                col1 = 1,
                                col2 = 2
                            };
context.tables.Add(newtable);

foreach (var b in data.tables.Where(x => x.col1 == 1).Union(new table[]{newtable}))
                        {
                            b.col3 += 3;
                        }