Web Forms :: Retrieve CheckBoxList Multiple Values In Code Behind

I am using a CheckBoxList in order for the user to select multiple items:

<td>
Shift Preference:(Multiple Selections Permitted)<br />
<asp:CheckBoxList ID="shiftPreferenceList" SelectionMode="Multiple" runat="server">
<asp:ListItem Value="">None</asp:ListItem>
<asp:ListItem Value="1st Shift">1st Shift</asp:ListItem>
<asp:ListItem Value="2nd Shift">2nd Shift</asp:ListItem>
<asp:ListItem Value="3rd Shift">3rd Shift</asp:ListItem>
<asp:ListItem Value="Weekends">Weekends</asp:ListItem>
<asp:ListItem Value="Overtime">Overtime</asp:ListItem>
<asp:ListItem Value="Holidays">Holidays</asp:ListItem>
</asp:CheckBoxList>
</td>

I need to read the value(s) chosen in code behind in order to execute a sql statement:

SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyDB"].ConnectionString);
connection.Open();
//Need to insert checked items into table
string sql = "Insert into shiftTable (ID, preference) values (" + id.text + ", " + shiftPreferenceList.selectedValue.toString() + ")

How would I iterate through the multiple selections and insert all checked values?