Installing the tree package

Hello,

In this kind of situation you need to:

1) Check on https://packages.ubuntu.com/fr/ if this package exists for your version of Ubuntu, and if so, which repository provides it.

The search yields:
https://packages.ubuntu.com/search?keywords=tree&searchon=names&suite=trusty&section=all

... and more specifically:
https://packages.ubuntu.com/trusty/tree

As you can see, tree is provided by the universe repository.

2) This repository is not listed in your

/etc/apt/sources.list

file, so you need to add it. To modify this file, you can refer to:
http://doc.ubuntu-fr.org/tutoriel/comment_modifier_sources_maj

... where you should type the command:

gksudo gedit /etc/apt/sources.list &

3) To know which line to add, simply refer to the documentation:
http://doc.ubuntu-fr.org/depots#depots_officiels

... and more specifically:
http://doc.ubuntu-fr.org/depots_trusty#depots_universe_et_multiverse

So you add the following to this file:

deb http://fr.archive.ubuntu.com/ubuntu/ trusty universe multiverse
deb http://security.ubuntu.com/ubuntu/ trusty-security universe multiverse
deb http://fr.archive.ubuntu.com/ubuntu/ trusty-updates universe multiverse

Save and exit.

4) Finally, just install the package:
a) launch your software center and get the latest updates (or

sudo apt-get update

),
b) optionally perform an upgrade (

sudo apt-get upgrade

)
c) then install the tree package (or

sudo apt-get install tree

).
http://doc.ubuntu-fr.org/software-center

Good luck!