title: write 2 dataframes in 2 different excel sheets
body: <p>I was trying something like this:</p>
  <pre><code>output_2df = pd.concat([installs, second_installs], ignore_index=True)
  output_2df.to_excel('./installs.xlsx',sheet_name='Answers')
  
  output_qdf = pd.concat([a_questionnaires, b_questionnaires], ignore_index=True)
  output_qdf.to_excel('./installs.xlsx',sheet_name='questionnaires')
  </code></pre>
  <p>Although it works without an error, when I open my Excel file, I only see the second sheet. The data from the first dataframe seems to be overwritten.</p>
  <p>Then I tried this:</p>
  <pre><code>writer = pd.ExcelWriter('./installs.xlsx', engine='openpyxl')
  
  # Append final dfs to one output_df
  
  output_2df = pd.concat([installs, second_installs], ignore_index=True)
  output_2df.to_excel(writer, sheet_name='Answers')
  
  
  output_qdf = pd.concat([a_questionnaires, b_questionnaires], ignore_index=True)
  output_qdf.to_excel(writer, sheet_name='Questionnaires')
  </code></pre>
  <p>However, in this case when I open my Excel file manually, I get an error that it cannot be opened since the file type is invalid.</p>
  <p>What's the correct way to write two different dataframes to 2 separate sheets in the same Excel file?</p>