dendrites on the film

Hello there!
After processing a EASTMAN DOUBLE-X Black & White Negative Film 5222, I am seeing dendrite like patterns on almost every other frame. The pattern doesn't really repeat in shape but location is repeatable and symmetric on both edges.
This is how it looks https://goo.gl/photos/UcEp6YF2ZjepV3yR8
Any ideas about what it could be? light leaks? Fungus? film degradation due to 'not so careful' storage? mechanical damage while loading on the reel?

electrostatic discharge

Whoa!
It did look like Lichtenberg figures. How and when would I have introduced those I wonder.

In winter humidity is low in your part of the world.
Fast film transport, best on non-conductive material.

The fact that the artefacts show up at the edges of the film make me guess it happened on a plastic reel or in a plastic camera.

But how can one unroll fast a nonprocessed film?
Maybe on fast winding. A Paterson-type reel can be wound fast. A Jobo-style reel still has the fingers as possible dischargers.

It was a plastic reel! I guess I'll have to run the humidifier for a while before I roll the film on.
This is unfortunate the way the pictures were ruined by one non-optical mishap right at the end of the whole sequence.
sigh...

IF it was the reel.

Maybe then a Jobo reel/tank would be better. THIS issue has not been discussed in the old tank-disputes as far as I know.

I agree with AgX said, that the fault appears to be caused by electrostatic discharge.
I did not understand if the film is packed in the original photo box or he was taken from a larger piece of film.
Simply said, if after factory the film has been handled (touched) by others.
As the picture shows, you need some friction between the film and the surface (edge) to have so lightning.
Due to production of fault I think could be a running system.

George