Summarize the following:
An Ash tree has a compound leaf structure, rather than a single leaf structure. Look for the thickened base of the stem, called a petiole, and decide whether there is a single leaf or 5 to 11 smaller leaflets that branch out from that point.  These 5 to 11 leaflets compose a single leaf. A Maple tree is an example of a single leaf tree that has one large leaf extending from the petiole. The only other tree that shares these two characteristics is a Boxelder tree. Yet, the Boxelder tree has three to five leaflets instead of five to 11. They are paddle shaped and look like small delicate leaves. They hang down in large groupings from the tree.   Don’t assume a tree without seeds is not an ash tree. Some types of ash are seedless. Seed clusters only form in late fall and early winter. Boxelder seeds are also clustered; however, they look like wings, rather than paddles.

Summary:
Find a branch with leaves on it. Combine the opposite branching and compound leaves to decide if the tree is an Ash. Find light green or brown clusters of seeds.