Time Series Plot for floating values
You can try this
wr.reset_index().plot(x='index', y=['a', 'b'], figsize=(10,5), grid=True)


The reset_index() will change the index back to column
The x = 'index' will use the date index as the x axis
The y=['a','b'] will plot both columns as two time series
figsize just tell the plot how big to be
grid=True will add a grid on the plot

You will need to give some extra 'love' to your styling to make it look exactly as your example.