Verse 20. "'The lofty and vigorous tree which thou sawest, the height of which reached the heavens...'" He explains the truth without insulting the king, so as to avoid appearing to charge the king with sinful pride, but rather with overweening greatness.
Daniel 4:20
20 The tree that thou sawest, which grew, and was strong, whose height reached unto the heaven, and the sight thereof to all the earth;
Commentaries
Daniel's wisdom is worth admiring: he did not say simply, the big tree, but grown to great size and strength—in other words, instead of being great from the beginning, you became great gradually, and instead of having strength from the outset, you gradually acquired it. Hence he goes further, "Because you have grown great and strong, your greatness has increased, you reach to heaven and your lordship to the ends of the earth." It was very fitting and appropriate for him to relate these things to heaven and earth: he said his lordship had reached the ends of the earth, that is, his authority, whereas it was not yet his lordship that had reached to heaven but his imaginings.
Source: COMMENTARY ON DANIEL 4:20-22