Are you booked in a standard view room? If so, it is unlikely that you will have a wonderful view, unless you are really lucky. I would simply request a room with as nice an unobstructed view as possible.
I have also had my view completely blocked by huge trees, so I know that it isn't fun, but it is much nicer than many standard views and not so bad when you are paying standard rates. It happened to me once when paying for a water view at the YC. I literally could not see anything at all but leaves! I also stayed in the Grand Floridian at Club Level and had an up close and personal view of a tree that completely blocked a view of anything else. I decided that at least it was private! LOL! So, although not your dream upgrade, it was still an upgrade to look at your tree.
The reality is:
Some standard rooms do overlook dumpsters, parking lots etc. and some people end up having to stay in them. Personally, i would be happy enough if booked in a standard view room to be upgraded to a 'resort view' of a tree. If you really don't want a standard view, it is possible to book resort view or lagoon view which will guarantee something nicer.
Good luck!