Ok, so I clicked on a tree and I see the diagram.
I clicked on the trunk node, but I see no Properties/materials.
Unity5 doesn't have a Tree Creator unless you're speaking of
Speedtree which has no nature category I can find.
I can see Kittens losing their limbs as I type.
The opposite actually - that's the tree creator you've pictured above. The SpeedTree creator on the other hand isn't built into Unity but a separate program costing $20/month.
The 'Branch material' shown above in the inspector (Mountain Ash Bark 1) is what you're after. Double-click it and you will see the base lighting etc. Similarly choose a leaf node to see its material.
The problem with adding a second directional light as you have done is making all your different trees looking good at the same time. Also if PP does put lighting control back into the course designer's hands (at the moment the game does the lighting), a second light will kill performance.