[Python] How to plot multiple Y axis using Altair on Streamlit?

I am wondering how I can plot multiple Y axis using Altair on Streamlit.

import pandas as pd
import numpy as np
import altair as alt
import streamlit as st

df = pd.DataFrame({
'name': ['brian', 'dominik', 'patricia'],
'age': [20, 30, 40],
'salary': [1000, 2000, 3000]
})

c = alt.Chart(df).mark_area().encode(
x='name', y=['age', 'salary'])
st.altair_chart(c, use_container_width=True)


The above example returns the following error:

SchemaValidationError: Invalid specification altair.vegalite.v4.schema.core.FacetedEncoding->0, validating 'type' [{'type': 'quantitative', 'field': 'age'}, {'type': 'quantitative', 'field': 'salary'}] is not of type 'object'

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