Rev 9:4
... they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads.

Code Words, below are scriptural references related to righteous men symbolized by "Trees":

Matthew 7:17
Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
18 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.
19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
20 Wherefore by their fruits ye shall know them.

Psalm 1:
1 Blessed is the man that walketh not in the counsel of the ungodly, nor standeth in the way of sinners, nor sitteth in the seat of the scornful.
2 But his delight is in the law of the Lord; and in his law doth he meditate day and night.
3 And he shall be like a tree planted by the rivers of water, that bringeth forth his fruit in his season; his leaf also shall not wither; and whatsoever he doeth shall prosper.

Jeremiah 17:
7 Blessed is the man that trusteth in the Lord, and whose hope the Lord is.
8 For he shall be as a tree planted by the waters, and that spreadeth out her roots by the river, and shall not see when heat cometh, but her leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit.

Ezekiel 47:
12 And by the river upon the bank thereof, on this side and on that side, shall grow all trees for meat, whose leaf shall not fade, neither shall the fruit thereof be consumed: it shall bring forth new fruit according to his months, because their waters they issued out of the sanctuary: and the fruit thereof shall be for meat, and the leaf thereof for medicine.

Revelation 22:2
In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations.

Genesis 2:9
And out of the ground made the Lord God to grow every tree that is pleasant to the sight, and good for food; the tree of life also in the midst of the garden, and the tree of knowledge of good and evil.

Revelation 2:7
He that hath an ear, let him hear what the Spirit saith unto the churches; To him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God.

Proverbs 11:30
The fruit of the righteous is a tree of life; and he that winneth souls is wise.

Isaiah 61:3
To appoint unto them that mourn in Zion, to give unto them beauty for ashes, the oil of joy for mourning, the garment of praise for the spirit of heaviness; that they might be called trees of righteousness, the planting of the Lord, that he might be glorified.

Jeremiah 11:19
But I was like a lamb or an ox that is brought to the slaughter; and I knew not that they had devised devices against me, saying, Let us destroy the tree with the fruit thereof, and let us cut him off from the land of the living, that his name may be no more remembered.

As in Revelation 9:4, below are scriptural references in which the word "Grass" symbolizes men:

Isaiah 40:
6 The voice said, Cry. And he said, What shall I cry? All flesh is grass, and all the goodliness thereof is as the flower of the field:
7 The grass withereth, the flower fadeth: because the spirit of the Lord bloweth upon it: surely the people is grass.
The grass withereth, the flower fadeth: but the word of our God shall stand for ever.

Psalm 103:15
As for man, his days are as grass: as a flower of the field, so he flourisheth.
16 For the wind passeth over it, and it is gone; and the place thereof shall know it no more.

1 Peter 1:
24 For all flesh is as grass, and all the glory of man as the flower of grass. The grass withereth, and the flower thereof falleth away:

Isaiah 51:12
I, even I, am he that comforteth you: who art thou, that thou shouldest be afraid of a man that shall die, and of the son of man which shall be made as grass;

)saom 37
1 Fret not thyself because of evildoers, neither be thou envious against the workers of iniquity.
2 For they shall soon be cut down like the grass, and wither as the green herb.

Psalm 92:7
When the wicked spring as the grass, and when all the workers of iniquity do flourish; it is that they shall be destroyed for ever:

John 12:
24 ... Except a corn of wheat fall into the ground and die, it abideth alone: but if it die, it bringeth forth much fruit.
25 He that loveth his life shall lose it; and he that hateth his life in this world shall keep it unto life eternal.

saiah 44:
3 For I will pour water upon him that is thirsty, and floods upon the dry ground: I will pour my spirit upon thy seed, and my blessing upon thine offspring:
4 And they shall spring up as among the grass, as willows by the water courses.

Genesis 1:11
And God said, Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind