I found a free tree generator https://www.cgchan.com/cantree but it doesn't make battlemap style top-down trees, just side-views, so I converted a bunch of renders into battlemap usable topdown trees. It has a very generous terms of service allowing the generator itself to be modified and redistributed, so certainly sharing some trees is permissible. Use it to make your own trees (you can upload bark, leaves, and flowers), just open it up in a raster editing program and repeat the piece you generated a few times to fill in the round and erase any weird bits. Or steal these ones.

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