How to create a active bugs trend chart

Hi everybody!

I'd like to create a Active bug trends, like this:

However, everytime that I try to create this, I always have this result

My chart always sum the quantity of bugs, not the trend

When I try to setup my chart, I have this screen

Note that I have the option Count. 

My question is: How to create a active bug trend chart?

I try this documentation but, no success: https://learn.microsoft.com/en-us/azure/devops/boards/backlogs/manage-bugs?view=azure-devops#monitor-bug-status-assignments-and-trends

Thanks for Advice

Mauricio