The ground was basically flat for a great distance in every direction. There was no need to make any decision to clear the road/trees. That was a very minor obstacle to a 737-800.
That's not quite true. I'm very familiar with that area and to be honest, if the pilots had any decision room left at that stage, they made the perfect decision as to where to land the plane.
About one kilometer earlier and they would have crashed on a dual-track railway line or the N200. The N200 is a dual-carriage motorway which sits in a depression at that point, with elevated entries and exits leading to a complicated 3-level junction ("Rottepolderplein") about 500 meters right of the flightpath. Immediately after the N200 they would find a few industrial buildings and then the "Ringvaart", a 40-meter wide canal with straight edges.
To their right, about 500 meters, would be the 6-lane highway A9, running almost exactly parallel. Again, the A9 sits at an embankment about 5-8 meters above the surrounding terrain, and is very busy at all times during the day. At the other side of the highway you'll find an industrial area.
To their left they would have some 300 meter clearance to some farms, and a little more clearance to the town of Zwanenburg. But this area is cris-crossed with small ditches, 3 meters wide at most, and a few farm roads that are slightly elevated above terrain level. And the farm roads are lined with trees whose stumps are about 30 centimeters in diameter.
A kilometer later and they would have hit the A9, who makes a 30-degree turn at that point bringing it under the 18R approach path. From memory, the embankment here is again about 5-6 meters high, since this 30-degree turn in the highway coincides with the "Haarlem Zuid" exit which is a rather complicated exit with multiple viaducts.
I agree that tops of the trees that line the N200 and the Ringvaart are not really obstacles to worry about in this scenario. But these canals and embankments, and the stumps of the trees lining the farm roads are. And the field where they crashed was virtually the only place where you could hope to put an aircraft down without hitting any of those.
Edited: Fokker52 provided this link:
from: 52.377339,4.711719 - Google Maps
Unfortunately Google Earth doesn't show the relative elevations of the various roads.