You can use the Artistic Media tool on the sprayer setting. I have CorelDraw X5 and it has a couple of tree sets in the Plants sprayer list. You could make your own list and then you just draw in a random pattern in the area you want the trees and you get a a bunch of them. You can edit the placement by editing the point of the line they are connected to or you can brake them apart and ungroup them and move them individually.
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