I have a 3D KMZ file that I created using extrusion in ArcScene and exported to KMZ using the Layer to KMZ tool. The features that I want to add for obstacle avoidance show up as 3D features in Google Earth, but when I try to import them into UgCS, no features show up. Has anyone else had any luck converting 3D files from ArcGIS to 3D KMZ?
I tried to import your trees_subset through the Add Building routine and got the same result, no joy. I tried importing them using the KML2UGCS droplet, but that is for routes and didn't result in the correct display. I will try some more and let you know. The 3D representation inside GE shows tree #4 significantly taller than the rest, its tree_ht attributes say 243 (ft I assume) while the rest are around 205, but it is 3 or 4 time taller.
Building import feature supports only KMZ import with embedded COLLADA 3D models. This means that KMZ (that is actually a ZIP archive with .kmz extension) file must contain one or several .dae files and one .kml file inside. KML file must reference those DAE files.
Currently we do not support 3D models implemented as a part of KML file (KML notation only) like your example. This feature will be added in one of our next versions.