You can already do that. When the tree is on the cursor press the i key and you can spray trees.
You can change the size of the trees by placing one then clicking on it and selecting scale, then you can pick it up again by selecting extract, and use i to spray them.
Primary Desktop:
i7 7700,k NV1070 8GB, 16GB 3200mhz memory, 1x 2TB Hybrid, Win10.
Secondary Desktop:
i5 4760k, NV960 2GB, 16GB 2333mhz memory, 1x 2TB Hybrid, Win10.
Laptop:
i3, Intel 4000 series graphics, 6GB memory, 1x 500gb HDD, Win8.1.