Here are some reference songs to help you identify the interval being played.
Minor Second – Für Elise (high note to low note).
Major 2nd – Happy Birthday.
Minor 3rd – Greensleeves.
Major 3rd – Oh when the saints.
Perfect 4th – We wish you a merry Christmas.
Perfect 5th – Twinkle, twinkle little star.
Minor 6th – The Entertainer.
Major 6th – Hush little baby
Octave – Somewhere over the rainbow.