Follow peace with all men, and holiness, without which no man shall see the Lord:
Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled;

-Hebrews 12:14-15

Germination of bitterness
Devastation of bitterness
Fruit of bitterness

And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice: And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.

-Ephesians 4:30-32
How do we get rid of bitterness?

Let God reveal it
Let grace remove it (Hebrews 12:15)
Let good replace it (Hebrews 12:14)