input: Write a function to add a header row to a CSV file.
  assert add_header_to_csv(["name,age,city"], [["Alice", 30, "New York"], ["Bob", 25, "Los Angeles"]]) == [["name", "age", "city"], ["Alice", 30, "New York"], ["Bob", 25, "Los Angeles"]]
  assert add_header_to_csv(["id,product,price"], [[1, "Apple", 0.5], [2, "Banana", 0.3]]) == [["id", "product", "price"], [1, "Apple", 0.5], [2, "Banana", 0.3]]
  assert add_header_to_csv(["date,event"], [["2021-01-01", "New Year"], ["2021-07-04", "Independence Day"]]) == [["date", "event"], ["2021-01-01", "New Year"], ["2021-07-04", "Independence Day"]]
output: def add_header_to_csv(header, rows):
      header_row = header[0].split(",")
      return [header_row] + rows