How to change column index in pivot_table

I have the code as below :
pivot = pd.pivot_table(df, values=“vco_freq_mhz”, index=[‘Corner’,‘VT’],columns=[‘Instance’,‘fcx’], aggfunc={‘vco_freq_mhz’: [min,max,np.mean,np.std]} )
st.dataframe(pivot)

And have the output as below :

But I expect the result as :

Is there anyway that I can change the pivot as I expect?
Thanks a lot for your help.