I made the nations to shake at the sound of his fall, when I cast him down to hell with them that descend into the pit: and all the trees of Eden, the choice and best of Lebanon, all that drink water, shall be comforted in the nether parts of the earth.
I made the nations to shake at ... his fall, when I cast him down to hell - Sheol or Hades, the unseen world; equivalent to 'I cast him into oblivion' (cf. Isaiah 14:9-11, "Hell from beneath is moved to meet thee at thy coming: it stirreth up the dead for thee, even all the chief ones of the earth").
All the trees of Eden shall be comforted because so great a king as the Assyrian is brought down to a All the trees of Eden ... shall be comforted - because so great a king as the Assyrian is brought down to a level with them. It is a kind of consolation to the wretched to have companions in misery.