What's the deal with people planting trees in Israel?

It might be because of the constant fighting. Maybe a sign of peace or maybe in tribute to people that have passed away.

Might be for Israelis living in another country to have some sort of connection to Israel or perhaps to beautify the desert looking land.

I think the latter, it is quite a deserty area.

Just to think, at one time, Israel was fill with trees.

there seems to be a religious component as well; see http://treestoisrael.org/

(Note I do not take responsibility for the political content of that page, merely pointing it out)