John Gill Commentary 2 Samuel 18:9

"And Absalom chanced to meet the servants of David. And Absalom was riding upon his mule, and the mule went under the thick boughs of a great oak, and his head caught hold of the oak, and he was taken up between heaven and earth; and the mule that was under him went on." — 2 Samuel 18:9 (ASV)

And Absalom met the servants of David
When his army was routed, he was in such a fright that he knew not which way to flee, and instead of flying from David's men, he fled in the way of them; but none of them attempted to slay him, nor even to stop him, but let him pass by them, knowing David's charge concerning him:

and Absalom rode upon a mule ;
as was common for great personages to do in those days, (2 Samuel 13:29) ;

and the mule went under the thick boughs of a great oak ;
and running full speed, Absalom could not guide him, nor stop, nor divert him from going under it:

and his head caught hold of the oak ;
either the hair of his head was twisted and entangled in the thick boughs of the oak; or rather his head was jammed into a forked branch of the oak:

and he was taken up between the heaven and the earth ;
hung in the air between both, as unworthy to live in either:

and the mule that [was] under him went away ;
and left him hanging in the oak.