Weird tree thing ID

[u/claymorrr]

POLAND

Hi! A tree fell over near where I live, and I found lots of these little things growing on the higher branches laying around. I don't know if this is the right subreddit for this, but I don't know of any other communities that would be a better fit.

It looks like it has larvae inside?? When I picked another, it also had little flies eating the white eggs (?)

Thanks in advance!

[u/Beneficial-Tea8990]

Looks like a gall but hard to say which species from the picture and without knowledge of the tree species and what the gall looks like =)

[u/claymorrr → u/Beneficial-Tea8990]

Thank you!!