I am following a tutorial for making an autumn road and I have come across a problem in which my trees are not spawning/growing out of my weight-painted vertex group all-of-a-sudden. They just appear randomly. Here is my blend file.
I had a look at your .blend file, and noticed the origin of the third tree in your group is way off. I assume you know how to change the origin, as the other 2 are correct, but just in case, this is how:
Enter Editmode > select the vertices at the bottom of the tree > Shift+S > Cursor to Selected > back to object mode > In the left panel click “set origin”, “Origin to 3D Cursor”