Hi Stig! Welcome to the forum!
I can help you with this one - those red spots are tree
galls, which don't necessarily mean there's something wrong with your tree
. Basically, bugs make them to lay eggs in. I wasn't sure what kind of tree
that was, so I couldn't find more in-depth information for you, but that should get you started. I'm sure someone else will come along that can help more - I'm still a newbie, but have a tree
with a zillion galls (on every leaf), which is why I knew what it was!