How to approach this with landlord

[NA Jones]

We are purchasing our first investment property which is in need of some rehab.  One issue is there is a tree on the edge of the neighboring property of which the branches are causing damage to the roof of our property.  We either need to trim the tree back significantly or remove it altogether.

The property next door is a 4-plex.  To my knowledge the landlord doesn't live in any of the units.

What is the best way to approach this situation?  Start writing letters or trying to get contact info from the tenants?

Would it be fair to ask the landlord to share in the costs of trimming / removal or is this something we should plan to entirely foot the bill for?  

Thanks in advance!