why does trailing icon appear near the middle of the listitle flutte code example

Example: flutter alignment listtile elements

Row(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: <Widget>[
      CircleAvatar(
        radius: 20,
        backgroundImage: AssetImage('assets/avatar1.jpg'),
      ),
      Expanded(
        child: Container(
          padding: EdgeInsets.only(left: 5),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              RichText(
                text: TextSpan(
                  style: DefaultTextStyle.of(context).style,
                  children: [
                    TextSpan(
                      text: 'hello :  ',
                      style: TextStyle(fontWeight: FontWeight.bold),
                    ),
                    TextSpan(
                      text:
                          'the comment comment the comment comment the comment comment comment comment the comment comment the comment comment',
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
      ),
    ],
  ),