Creating a line graph with recurring Y values
 

Hello, I am a bit new to Excel and I am trying to create a line graph that tracks student progress over time. Setting up the Y-axis is what creates a problem for me; I'm trying to track what level (Level 1, Level 2) each student is on and for each level, it is divided up into 4 intervals (50, 100, 150, 200). Maybe the picture I have provided will better explain what I'm trying to do. Thank you.