In August 2015 I successfully install Postgresql 9.5 in Ubuntu 14.04 Trusty Tahr following the instructions from the official Ubuntu page (to which I was led from this article).
Basically I just selected Trusty (14.04) as an option in the drop-down menu as shown in the figure below:
…and then (after adding the repository and key) I did:
sudo apt-get update sudo apt-get install postgresql postgresql-contrib… in order to get the latest stable version.
$ sudo su - postgres postgres@beorn:~$ psql psql (9.5.4) Type "help" for help.… right afterwards revealed that the version that was installed was in fact 9.5.4.