create rootCurve: Create the main tree trunk.
create branchCurve: You must be create the main tree trunk, and then create branchCurve.
use curveShape: use curve to control root shape: 
select Curve priority:
selset Mesh priority:
set pivot to root: set curve pivot to curve.cv[0].
display mesh Color: show face color on slitTreeMesh.
create Slit by shader: Automatically creates five rendering layer. see slitLayer Attribute.
You must be set light shader type to ray trace shadows: 
Add displacement: Add displacement to slitSG. Work on all layers.
slitLayer
slitLayer Attribute:
SlitInfo Attribute:
Color: please don't modify it.
Diffuse: control tree shader diffuse
Ground name: define gound name
Plane: If the ground is flat, please select it, Will increase the speed.
Height: Specifies the height of the ground.
SlitDisplacement Attribute:
Color: Add displacement texture.
Factor: Control the noise level.
If you want to get better effect, set sample rate to 32,
but will increase render time.