How to read multiple csv files into pandas with streamlit's selectbox

How can 2 selectboxes 1st with alphabets and the 2nd with the names that start with that alphabet

1- I used the following code to create a list of CSV file names

import os
import stremlit as st

path = "/home/zhamane/streamlit/Streamlit_tutorials/data"
li = [os.path.splitext(filename)[0] for filename in os.listdir(path)]

for example, I have 3 files in ‘data’ folder (all_stocks_5yr.csv, auto-mpg.csv, clean_auto_mpg.csv) it will return a list

[all_stocks_5yr, auto-mpg, clean_auto_mpg]

2- i use selectbox from stremlit to select those files

select_event = st.sidebar.selectbox('Choisir des indicateurs', li)

But I want to create 2 selectboxes 1st with a list of alphabets created from the initial alphabet for each file name (in our example)

[a, c]

and when I select for example a the 2nd list will show me all the names that start with a

3- after that i want to read the file selected with panda

df = pd.read_csv("path/{select_event}.csv")

As per my understanding of the problem,