title: how append dataframe to dataframe with duplicate id
body: <p>i have a dataframe df1</p>
  <pre><code> id  Name  City   type 
   1   Anna  Paris   AB
   2   Marc   Rome   D
   3   erika  madrid AC
  </code></pre>
  <p>and a dataframe df2</p>
  <pre><code> id  Name  City   type 
   1   Anna  Paris   B
  </code></pre>
  <p>and a dataframe   df3</p>
  <pre><code> id  Name  City   type 
   1   Anna  Paris   C
  </code></pre>
  <p>i want to append df2 and df3 to df1 , this is my expected output :</p>
  <pre><code> id  Name  City   type 
   1   Anna  Paris   AB
   2   Marc   Rome   D
   3   erika  madrid AC
   1   Anna  Paris   B
   1   Anna  Paris   C
  
  df1  = df1.append(df2)
  df1  = df1.append(df3)
  </code></pre>
  <p>but the dataframe add only the last row and  delete the other rows  with the same id</p>
  <pre><code> id  Name  City   type 
   2   Marc   Rome   D
   3   erika  madrid AC
   1   Anna  Paris   C  
  </code></pre>
  <p>i mtrying also concat</p>
  <pre><code>df1= pd.concat([df1,df2,df3], join='inner')
  </code></pre>