Thunder Shock

A blue thunder bolt, comes down from the heavens toward a creature within range, forming a sustained arc of lightning between the sky and the target. Make a ranged spell attack against that creature. On a hit, the target takes 1d8 Thunder damage, and on each of your turns for the duration, you can use your bonus action to deal 1d8 Thunder damage to the target automatically. 

At Higher Levels. This spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).