Hi Diane, are you able to upload a picture of the insects on your tree leaves? We can make much better recommendations with a good identification. The most likely "little black bugs" might include aphids, box elder bugs, or seed bugs. These would be handled differently.
Thank you!
Nicole

Thanks, your picture was so helpful. Those are a kind of Maple aphid: https://en.wikipedia.org/wiki/Periphyllus
More info about them from OSU here: http://oregonstate.edu/dept/nurspest/Periphyllus_aphid.htm
and in the above link, a link to the PNW handbook, which has suggestions for management. With a newly planted tree, a soap spray may be sufficient fore control, but will likely need to be applied multiple times.

I hope this is helpful! Thanks for responding with great images that made ID easy.
Sincerely, Nicole