The Tree Shape spell indicates that a Druid (or other character with the spell or ability) can turn into a "large living tree or shrub" and that the "exact type of tree, as well as its appearance is completely under [that character's] control":
This spell allows you to assume the form of a Large living tree or
shrub or a Large dead tree trunk with a small number of limbs. The
exact type of tree, as well as its appearance, is completely under
your control.
The Entangle spell indicates that "tall grass, weeds, and other plants" can be used for the effect:
This spell causes tall grass, weeds, and other plants to wrap around
creatures in the area of effect or those that enter the area.
My main question is: can a Druid in tree form be used in combination with another character casting Entangle, in order to produce the same effects as Entangle, but in an area where there is no naturally-occurring other vegetation (of significant note), for example in a building?
If yes, could the Druid choose to be a thorny bush and gain the additional effects mentioned in the Entangle spell?
If the plants in the area are covered in thorns, those in the area
take 1 point of damage each time they fail a save against the entangle
or fail a check made to break free.
EDIT: To clarify, the Entangle spell would be cast by another character, not the Druid.
Best Answer
RAW it is probably a No.
Tree shape does not turn you into a plant. It just magically disguises you.
However, this is something you should talk to your GM about.