As for operation:
I've been recommending Onyx for a long time, but it is only since Archicad has the LightWorks engine that we can do a city block of 3D Onyx trees.
Starting with an existing botanically accurate model from the Onyx library of conifers, broadleaf, palm, bamboo or flowers, any parameter can be adjusted to make a model unique.
When exporting the model to 3Ds, filters permit polygon reduction by eliminating smaller elements like stems (Got no stems, got no seeds, Acapulco Gold, that's tree) and flattening leaves. See attached image for export dialog.
We all know that too many polygons can kill a rendering and trees have lots of them. In fact, if mediocre World War 1 poet Joyce Kilmer was alive today, his poem "Trees" would read:
"I think that I shall never see
as many polygons as in a tree."
My Onyx tricks are:
flat leaves.
larger, but fewer leaves
only export the leaves, larger branches and trunk with only five sides.
Unless you make a special translucent, speckled and perforated material to soften edges, leaves CAN look like the shattered emerald we are accustomed to in Archicad trees. Softness counts.
Onyx uses the standard xyz orientatiion and Archicad does not, so you need to tweak your 3DS import or the trees come in laying down.
I also recommend exporting the foliage separately from the branches and trunk so that you can rotate them against each other to give the impression of variety in a street tree line. It is also easier to change materials in archicad if you do this.
Dwight Atkinson