Adam Clarke on Esther 5:14

Let a gallows be made of fifty cubits high - The word עץ ets, which we translate gallows, signifies simply wood, a tree, or pole; and this was to be seventy-five feet high, that he might suffer the greater ignominy, and be a more public spectacle. I believe impaling is here also meant. See the note, Est 2:23 (note).

In former times the Jews were accustomed to burn Haman in effigy; and with him a wooden cross, which they pretended to be in memory of that which he had erected for the suspension of Mordecai; but which was, in fact, to deride the Christian religion. The emperors, Justinian and Theodosius, abolished it by their edicts; and the practice has ceased from that time, though the principle from which it sprang still exists, with the same virulence against Christianity and its glorious Author.