What is this on Willow

[MothMan]

Is anyone able to tell what the cause of this formation on Crack Willow (Salix fragilis) is?

Looks like an eruption of small twigs.

I've checked the GB gall key and cannot find anything that resembles this. Does anyone have any idea?

[Palustris]

It looks either like a witches broom which is caused bt 'mechanical' dmabe to the tree. So something dmages a bud and the tree reacts by producing a multiple set of shoots. OR it could be a fungal growth, though I have to confess I have never seen one grow like that before. Is the thig made up of twigs or something else?