How to make the trees on the grid not through the grid? (Speedtrees, origin problem) The trees and the grid are joined somehow and I don't know how to undo this.
This is the tutorial I'm following Large Scale Forest Flyover in Blender 2.8 - Quick and Dirty
1:30 is what applies to me the trees appear halfway through the plane and I don't know how to fix this. I want the trees on the plane NOT halfway through.
The orange dot in the center is the object's origin (the root of your tree). To move it down to the Z=0 position (the ground), switch to Edit mode and move all vertices of the mesh up.

Another option is to use the 3D cursor (and Shift+S menu), or move the origin directly in Object mode.