Here we see very clearly that the tree in his dream points to a human being. It concerns a human being who needs to experience that whoever exalts himself will be humbled by God. His glory is even broken down to such a low point that for quite some time he will resemble no more than an animal. For further explanation see Daniel 4:23–26.
16 Let his mind be changed from a man’s, and let a beast’s mind be given to him; and let seven periods of time pass over him.