iReport ,why i can't place group of nods. group ander group.

Question

Hi im new to iReport and i try to do simple thing without much success i have this xml

<addressbook>
    <person>
        <name>ETHAN</name>
        <phone>+1 (415) 111-1111</phone>
    </person>
  <person>
        <name>CALEB</name>
        <phone>+1 (415) 222-2222</phone>
    </person>
    <car>
    <firm_name>fiat</name>
    <year>1984</year>
    </car>
    <car>
    <firm_name>GMC</name>
    <year>1986</year>
    </car>
</addressbook>

and i want to display the group of nods first and under it the group of data but when i place in the Detail band the $F{name} field and under it the $F{firm_name}
like this :

$F{name}
$F{firm_name} 

the PDF output show me :

ETHAN
fiat
CALEB
GMC

but what i need it to be :

ETHAN
CALEB
fiat    
GMC 

what im doing wrong here ?
Thanks