Ever since the Greenwood Ranger kit in 2nd Edition, I have loved the idea of ranger’s essentially BECOMING a part of nature. Here is my take on it.
At 3rd level, you can subsist on sunlight. You do not need to eat or drink as long as you spend at least 6 hours outside. Also, you can spend Hit Dice while traveling every 2 hours as long as you are not fatigued and not traveling at a fast pace. Lastly, your Hit Dice increase to d12s while in sunlight, which does not retroactively affect your total hit points.
At 7th level, your skin becomes thick and bark-like. You gain resistance to nonmagical bludgeoning and piercing damage.
At 11th level, you can use an action to become indistinguishable from a normal tree while you are motionless. While in this form, you are immune to affects that would force you to move or knock you prone. You revert to your true form if you take damage. You can also communicate with plants as if by the speak with plants spell.
At 15th level, you let no strike go unanswered. When you take damage from an enemy that you can see, you can use your reaction to make a weapon attack.