It has a shape like a cedar tree.
How would you describe a hippo tail in 7 words?
I can't find the evidence on the net, but I believe I've seen video of mad hippos stick their tail straight up and wave them around.
Looks like a cedar tree to me.
And you're still ignoring the rest of the chapter that obviously describes a hippo.
You're stretching, here. It's obvious the distinguishing characteristic of the Cedar tree is its size, not its shape. The normal inference to anyone painting the analogy would be size.
If I were to say a tail like a Redwood, there's no way you would think I was describing something straight and red with a green tuft at the end. You'd immediately visualize something massive and huge.