How to make a stacked bar chart with specified bar heights in seaborn

Question

I have a pandas dataframe like below. In the dataset, there are 3 segment (A,B,C). Column SEG_PCT is segment pecentage value. Each Segment has two groups. Column GRP_PCT is pecentage value for each group within each segment.

I need to plot a bar chart (using seaborn or pandas plot), with 3 stacked bars (A, B, C), with bar height as value of column SEG_PCT. Within each stacked bar are the GRP with GRP_PCT value.

I'm new to seaborn and pandas plot. Have no idea how to make this kind of plot. Thanks a lot in advance.

df = pd.DataFrame({'SEG': ['A', 'A', 'B', 'B', 'C', 'C'],
              'SEG_PCT': [0.6, 0.6, 0.4, 0.4, 0.2, 0.2],
              'GRP':['GRP1', 'GRP2','GRP1','GRP2','GRP1','GRP2',],
              'GRP_PCT': [0.7, 0.3, 0.6, 0.4, 0.1, 0.9]               
              })

    SEG  SEG_PCT   GRP  GRP_PCT
0   A      0.6  GRP1      0.7
1   A      0.6  GRP2      0.3
2   B      0.4  GRP1      0.6
3   B      0.4  GRP2      0.4
4   C      0.2  GRP1      0.1
5   C      0.2  GRP2      0.9