Plant Identification

Hi,

I'm trying to identify this plant which is inside my neighbours tree. I'm not sure if it's actually part of the tree or growing in it?

Each year flocks of starlings feed on it, whilst I've also spotted a couple of Blackcaps on it.

I'd like to get some of it for my garden, as I fear one day my neighbour might cut it down and it will be gone forever. 

Thank you