tree N=x parameter extraction

Hello everyone! I have a quick question, perhaps someone can help me out. I am trying to extract from  a tree the length of a tree branch (i.e the integers after N = ).

For example, if I have a tree

{0;0}  (N = 3)

{0;1}  (N = 2)

I'm looking to get as result a list

3

2

I'm sure there must be an easy way, but I just can't seem to extract this info. I've tried extracting it as a sub-string from param viewer, but param viewer seems only to forward the branch info inside the curly brackets on to a string component.

Any help is very much appreciated!

Thanks,

Daniel