Mergesort recurssion tree depth...logs I think some of the log properties are flying over my head but I'm trying to understand how the depth of mergesort is...

$1 + \log_2 n$

I understand that to get the depth, you would have to divide $n$ by $2^x$ but I don't how this leads to the above.

It's probably some simple log principal but I'm not sure.
The merge sort algorithm creates a complete binary tree, which has depth 'd' and at each level, a total of n elements.
So, 2d ≈ n, which implies d ≈ log2 n