How to resolve the issue of big pine trees coming from outside private apartment complex boundary to my property

You might have a valid civil claim for trespass and/or nuisance, particularly if the trees are that serious of an encroachment that they are interfering with the use and enjoyment of your property.  You may also reasonably trim the encroaching branches, but you must be very careful.  If you damage the tree, you can be held liable by the other property owner.  In 1994, "tree law" was changed in the case of Booska v. Patel - a neighbor does not have the absolute right to cut encroaching roots and branches so that they end at his or her property line.  Damages for injury to a tree can mount up because the statute in California allows for "treble" (triple) damages and more. Since you have already tried to work with the City, your best option may be a lawsuit for trespass/nuisance and seek an order from the Court abating the nuisance properly.  You will need a tree expert to write a report that your attorney will submit to the Court.  Take lots of pictures showing the tree encroaching, the droppings, etc.  You may also want to get an opinion from a realtor about diminution of value in your property. If this is a northern California situation, call me.  I have handled prior tree cases.