Circle of the Grove

Some druid circles attune to forests even more than most druid circles. They actually see themselves just as much as a part of the forest as the trees. These shepards of trees do not travel much outside their forest exept for when they have no other choice.

Tree shape

When you choose this circle at 2nd level, you gain the ability to use Wild Shape on your turn as a bonus action rather than as an action. 

Additionally you can use your Wild Shape to take form of a tree.

When you use your Wild Shape to take the form of a tree your armor class becomes 16, your movement speed 0 and you gain temporary hitpoints equal to 5 times your class level. You can change back your form as a bonus action or you automatically change back if you become unconscious. While you are in the form of a tree your size is large and you cannot take the attack action or cast any spells that need a verbal or somatic component. You however can cast certain spells without expending spellslots without any need for any of the spell components. You are not required to have these spells prepared.

the spells you can cast this way are:

Entangle, Spike Growth and Thorn Whip

Thorn Whip

Whenever you use wild shape to transform into a tree you have acces to the Thorn Whip cantrip.

One with the Forest

At 3rd level, you gain proficiency in nature if you did not already have it. Whenever you make a nature skill check you may double your proficiency bonus for that skill check..

Unrooted

Starting at 6th level, you are capable of transforming yourself into magical plants. You may use your Wild Shape feature to change yourself into an Awakened Tree. While in this form you can still cast spells and you can also pass through plant based difficult terrain without being hindered in your movement and without taking damage from these plants if they have thorns, spines, or a similar hazard. This includes magicly created difficult terrain. All other rules for wild shape remain the same.

Overgrowth

When you reach 10th level, you can make tall grass and roots sprout out of the ground wherever you are. As a bonus action while standing on the ground you may create difficult terrain in a 15 foot radius around you.

Awakened Forest

When you reach 14th level, you can encourage plants to fight for themselves. You can use the Awaken once on a plant per long rest without the need of any spell components. When you use this feature to cast awaken the casting time of the spell is reduced to 1 hour. The effects of the awaken spell cast by this method end as soon as you use this feature again.