³⁵ I have seen the wicked in great power,
And spreading himself like a native green tree.
³⁶ Yet he passed away, and behold, he was no more;
Indeed I sought him, but he could not be found.

Power - tyrannical.  mighty, oppressor, strong

Spreading - flaunting, exposing

Tree - spontaneous growth, native (tree or persons).

Passed away - was gone, disappeared, taken away, perished

Sought - searched, required

One who was prosperous and mighty and wielded vast power not for purposes of benevolence, but for injustice, oppression, and wrong. It was a "wicked" man that was thus powerful. And spreading himself - The word used here means properly to be naked; to spread oneself abroad. It is applied here to a tree that seems to spread itself out in every direction - sending its limbs aloft, and its branches far on every side "a native tree;" that is, a tree that grows in its own soil, not transplanted. One born in the country, not a foreigner: His life has been spent in tranquil scenes, where everything seemed to be stable and secure; what his end will be, the psalmist states in the next verse.

 "He was gone;" he had disappeared. Neither his prosperity, his greatness, nor his wealth, could provide him with a place on earth. 

And lo, he was not - He was no more; there was no longer any such person: The word "lo" implies that there was some degree of surprise, or that what had occurred was not looked for or expected. The observer had seen him in great power, flourishing, rich, honored; and, to his astonishment, he soon passed entirely away.

Yea, I sought him, but he could not be found. The psalmist says that after the most diligent search, he could not find him. He had disappeared entirely from among men.

(From Barnes Notes)