import altair as alt

df = pd.DataFrame(dict(time=['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
                        product_A = [20, 35, 30, 35, 27, 43, 24, 34, 14, 27, 22, 50],
                        product_B = [25, 32, 34, 20, 25, 34, 54, 23, 43, 33, 27, 29]))


alt.Chart(df).transform_fold(['product_A', 'product_B'],
  as_=['column', 'product']
).mark_bar(cornerRadiusTopLeft=3,
    cornerRadiusTopRight=3).encode(
    x='time:N',
    y= 'product:Q',
    color = 'column:N'
)