I was actually a little disappointed that there were not more examples to be seen down there. In general I find these monuments in rural areas, perhaps with more of them in areas where fraternal lodges were more prevalent. Iowa should be prime hunting ground. I will with difficulty not joke to excess about how folks in that square, flat state may not actually know what trees look like!
But lets have a look at a couple of odd ones.
I must admit that my usual visual scan of the cemetery in Postville Iowa did not detect this one at first. The shape is weird for one thing. It almost looks like an ear of corn. Note the stone pattern of the base. This is seen on earlier monuments, mostly from the 1870s. The main body of the monument clearly has bark pattern and cut off branches. But it oddly is semi rectangular instead of round. I think this carver was just not familiar with the style. Or maybe he was just not very good.
On the other hand....
Check out this beauty from Cedar Rapids. The top view shows the dimensions of the Novak family plot with the subsidiary tombstones front and center. I did not get a shot of them but I assume the back markers are just that, markers for the back of the plot. You would have to be in Bad Graces indeed to be buried facing away from the rest of your tribe!
A closer view. These Tree-Cabin hybrids are rare and when you find them they are always top quality work. This makes three we have found in Iowa, so this sub type at least seems to be more common down there than elsewhere.