Pinus densiflora 'Pendula'.

Pine needles attach to the branches in fascicles (or bundles). They typically are in bundles of 2-5 needles. How many needles per fascicle does your tree have?

From the picture, I'd probably guess the same as bboy, but note that P. densiflora 'pendula' (weeping Japanese red pine)has needles in 2/fascicle. But, there are other possibilities such as: P. strobus 'pendula' which has needles in 5/fascicle (weeping white pine - but I would expect a taller specimen if it is truly 20 yrs old). For identification see if you can figure out the # of needles per fascicle.

As far as keeping it...it would make an interesting specimen tree due to its form and such. If you can plan the deck around it, it could look neat to have a good gap (1-2') between the deck and the tree, and then have blue stone pebbles/rocks beneath. I personally like the contrast between the blue stone and the green foliage.