petiterose, this is a baby tree, my husband and I call them wild trees, since we do not know the correct name. We took out over 12 of these trees from our alley fence line when we moved into our house in 1979. I kill the young seedlings by digging with a shovel, cutting off as far as I can go, and then applying purple cap round up to the exposed root. That is the only way we have been able to control these trees. They grow in clusters, not very full, you probably have a tree in your neighborhood, that is supplying these gifts for you. Barbra,

I'm not positive, but I think that they might be Brazilian pepper-tree (Schinus terebinthifolius) which are very pretty in the fall, but considered very invasive.

Hmm. I'll have to look around to see if anything nearby sports similar foliage.

Any other thoughts are still more than welcome. :)

Looks like an Ash tree. Seen many of those come up before...

Take it to your county extension office. They should be able to identify it.

Now, there's a thought! :)