“The cedars in the garden of God could not hide him, the fir trees were not like his boughs, and the plane trees were not as his branches. Nor was any tree in the garden of God like him in his beauty. I made him fair by the multitude of his branches, so that all the trees of Eden that were in the garden of God envied him.”
This may be hyperbole based on ideas about the trees in Eden, to stress his supreme greatness, or it may be that Lebanon was popularly known as ‘the garden of the gods' because of its splendid trees (and thus ‘the garden of Eden' to Israel), and was therefore seen as the measure by which all trees should be measured. Either way Pharaoh and Egypt are seen as exalted above them all because of their great strength, fruitfulness and power, and it was by the hand of Yahweh (‘I made him fair'). As over everything else Yahweh was over this. But being so had given them a great responsibility and in this they had failed.
There may here be a comparison with Tyre. That too had claimed great beauty and to be connected to the garden of the gods (chapter 28). That too had many offshoots. But if so here God is declaring that even great Tyre could not compare with Egypt, none in Tyre could compare with the Egyptians.