~22 meters (72 feet)

And how do I know it?

There are several ways to measure the height of tall things. I used pretty much the first one, except I chose a stick instead, equally long as is the length of my arm held stretched forward, to get the 45 degree angle measured. I also have an old 15 meter tape measure, which helped a lot to get the distance measured more accurately.

UPDATE: The tallest tree in Finland is 47 meters (in 2018). The source in Finnish:
yle.fi/uutiset/3-10524561

Contribution for The Sunday Challenge, Scavenger Hunt 2020 Challenge.