Tere, r/Eesti! Any military history buffs here able to help identify a uniform?

I was going through some very old photos given to me by my vanaema, and came across a great portrait of her father in uniform. Given his age in the photo, I would assume this was approximately around WWI, so I assume it’s an Imperial Russian Army uniform - the circular cap badge looks similar to what I’m seeing in basic Google searches for WWI-era uniforms. My question is about the cross badge - does anyone know what it represents? I figure it might be the emblem of a certain regiment, perhaps an all-Estonian one, so I wanted to ask in case anyone here might happen to recognize it. Aitäh, and my apologies for posting in English!