Well, a genogram is different than a basic family tree, right?
I've never seen an actual genogram template, but you never know, maybe
someone will pop in with a link to one. I suspect you'll have to create your
own using the autoshapes on PPT's drawing menu. Or use Visio, if you have
it. It was designed for drawing diagrams, and you and put your final product
into your PPT slide very easily.