Convert common sql column value to xml node

Let's say I have a data set like this:

|Group|Value|
|-----|-----|
|  A  | 123 |
|-----|-----|
|  A  | 234 |
|-----|-----|
|  B  | 123 |
|-----|-----|

And want to convert it into XML like this:

<Groups>
    <Group Name="A">
         <Values>
              <Value>123</Value>
              <Value>234</Value>   
         </Values> 
    </Group>  
    <Group Name="B">
         <Values>
              <Value>123</Value>
         </Values> 
    </Group>    
</Groups>

I've tried using something along the lines of:

   SELECT  
         [Group] AS "@Name"
        ,[Value] AS "Group/Values/Value"
    FROM [Tablename]
    FOR XML PATH('Group'), ROOT('Groups')

But what I'm getting is:

<Groups>
    <Group Name="A">
         <Values>
              <Value>123</Value> 
         </Values> 
    </Group>  
    <Group Name="A">
         <Values>
              <Value>234</Value>   
         </Values> 
    </Group>  
    <Group Name="B">
         <Values>
              <Value>123</Value>
         </Values> 
    </Group>    
</Groups>

How can I combine these nodes based on the data in the first column?