Concise Bible Dictionary:
Olives
This occurs but once in the AV (Isa. 41:19), but the Hebrew (ets shemen) occurs also in 1 Kings 6:23, where it is translated “olive tree”; and in Nehemiah 8:15, where it is rendered “pine branches”; “olive branches” being mentioned in the same verse would seem to indicate that the “tree of oil” is distinct from the olive tree. Some believe it to be the Balanites Aegyptiaca; but others identify it with the Elaeagnus angustifolius.
Olive Trees