ok
there are couple of ways to do this
it all depends on what you tree looks like and how you want to set it up?
do you want it to be interactive?
i would firstly draw out the tree by hand first and then move on from there
ok say i have a tree
you can make the first slide the entire tree, and then add in pictures of each branch (family) as a little picture on that main tree, from there you can make each picture clickable and that would take you to the next slide with that branch....and then at the bottom you can add interactive arrows which would bring you to the next slide or the previous slide, or an icon which would take you back to the main tree slide....etc etc
i hope you understand what i'm trying to say
if you require more infromation i'm happy to provide it