In his highly anticipated (by the NSA oppressed among me) book Glory in our Midst (a commentary-ish thingamabobber on Zechariah), Kline, after a series of brilliant points, missed the one central point that I have ever gathered from that particular book.
When the rider (Christ) is mentioned as being among or between the trees, there is a ton of symbolism. Yes, the trees represent the people of God in front of the sea of their enemies, and no, I didn't see it. Yes, the trees (Myrtles are evergreens) represent the verse in Revelation speaking of the trees of life. Don't recall seeing that one either. Yes, the menorahs, yes the olive trees, and no, I didn't see any of these either.
However, the central theme of God between trees in all of Scripture is when He Is on a tree, and that is a symbol that Kline inexplicably (and almost inexcusably) misses in this vision.