This explanation is going to be a bit wordy so bear with me.

What just happened is the final phase of the Parasyte Tree's ability.

The way it works is that every time an employee does work with the Parasyte Tree, they receive a blessing that restores SP over time and improves their success rate when working with other abnormalities.

However, you must be careful with these blessings as if five employees are blessed at the same time, all blessed employees will panic and run around wildly, trying to spread out over the facility.

After some time, they will stop and turn into the tree-like being you see in the GIF, known as a sapling. After they transform, they will begin emitting a toxic gas that deals white damage(sanity damage) to anyone in the same room. Anyone that panics from this will exhibit the same behavior and become a new Sapling.

Actual footage of plant-based bioweapon, Advance Wars: Days of Ruin