Learning Model 003

I'm learning how to define modules in OpenSCAD. This model is my exploration of how to define a forest of trees as modules of treelines which are sets of trees, made from boxes and cylinders.



Instructions
module leaves(){
cylinder(20,4.8,0);
}
module box(){
cube([5,10,15]);
}
module tree(){
leaves();
scale([0.5,0.5,0.5])
translate([-2.5,-5,-15])
box();
}
module treeline(){
translate([20,0,0]) tree();
translate([10,0,0]) tree();
tree();
}
module forest(){
translate([0,20,0]) treeline();
translate([0,10,0]) treeline();
treeline();
translate([0,-10,0]) treeline();
translate([0,-20,0]) treeline();
translate([-2.5,-22.5,-9]) cube([25,45,2]);
}

forest();