Help my Cherry tree! Split trunk

Hi all,

I am looking for some help and advice. I have noticed my patio cherry tree seems to have developed a split at the bottom of the trunk, does anyone know what causes this and what I can do to help repair it?

I also noticed a tar like substance on one of the leaves. Any ideas what it could be?

I have looked both up on the internet and have come across so many answers that I'm not sure whats what. I have attached some photos.

Thanks in advance