It is thou, O king, that art grown, and become strong
Here begins the interpretation of the dream: the tree was an emblem of King Nebuchadnezzar, of his greatness, and growing power and strength: for thy greatness is grown, and reacheth unto heaven;
he overtopped all the kings of the earth, exceeding them in honour and power, and aspired to deity itself; (See Gill on Daniel 4:11) and thy dominion to the end of the earth;
as far as Hercules's pillars, as Strabo F17 says he came. Grotius interprets it, as far as the Caspian and Euxine sea, and the Atlantic ocean.
F17 Geograph. l. 15. p. 472.