how did the hanging tree song manage to survive?

Does anyone else find it weird if it there was still people who remembered the song and sang it with snow still charge? How was it did it get passed down from one generation to the next without the people being persecuted ?he obviously hated it and would have not been okay with people just singing it ,given what it symbolises and what it reminds him of. The song survived for 64 years how is that even possible under snows's dictatorship.