In your tree test, it seems an AA problem.
In exterior with a lot of trees, you must to use only PT+PT with low GIvsAA (more passes in the same amount of time).
In this way, you will have more AA Samples, because you don't need a lot of GI samples.
In the fly-through interior, you have to use PT+UHD, but you have to pre-caluclate UHD with "Try to Load + append" option.
If you will use "calculate from scratch", the UHD will change, frame by frame, the sampling and you could have flickering.
Obviously, in interior scenes, GIvsAA should be 10-20, depending the complexity of the scene (a lot of GI or a lot of DOF)