Question
i have a very small lot and just put in septic system the kind where you can see the green lids on the tanks i have no trees and i would like to plant some but i don't know what kind to get i have to get some that don't have big root systems what kind can i get

Answer
If, as you say you have a "very small lot", I would suggest NO trees.  Here is a good website for septic system information:

http://septictankinfo.com/Machmeier_Care_n_Feed.shtml

It is not just the tank, but also the leach lines, clan-outs, and service pipes that can get clogged by roots.

IF you cannot live without a tree on your "very small lot", then I would suggest the following root-friendly trees (please check which is best for your USDA zone):

Bradford Pear, apple, peach, plum (flowering or fruiting), apricot, or with a bit of room, the Sweet Gum.

Plant them no closer than 10 feet to any pipe, leach field, tank, or clean-out.

Hope it helps ~Marc