This isn't the first time I've made a crossword with a similar theme and with this exact shape, and it might not be the last. The meta answer is the name of a song.
Explanation: Only seven letters in the grid are from the range A-G - those letters are placed in order as per on a musical staff. Reading (or singing) left to right, the tune is either 'Twinkle, Twinkle, Little Star' or the 'Alphabet song', your choice.
For the aforementioned previous crossword, see here.