It looks like what has been described as a "tree" but I wouldn't know having lived my entire life on the prairie nowhere near a river or a stream and never having seen one.
A few years back, I was visiting in Massachusetts, and my host asked about having trees in Nebraska. I said to him, “don’t you get claustrophobic here; you cannot even see the sky!”
It's a tree. It fell off of a truck taking it to the Ripley's "Believe It Or Not" museum in Lincoln.