I currently have a tree diagram that shows the probabilities for certain paths in a game. The tree diagram first branches into four possibilities and then another four possibilities for each of the beginning four, making a total of sixteen possibilities (numbered outcome 1 - 16). I would like to know the proper mathematical notation or term to address the "root" of the branches that lead down to outcome 4 - 8. I have called the starting point of the whole tree diagram the "root" so I feel like it is confusing to term the branches of outcomes 4 - 8 that merge as another "root". Currently I am referring to its probability as "P(Outcome 4|8)" but is that an acceptable way to refer to it?
Edit: Now that I learned the definitions, my problem is that I do not know how to call the node on the 2nd level that branches out into leafs (outcomes which are on the third level) 4 to 8.