How to display nested Collections

I'm a new user of displaytagLib 1.1, i'm on a school web project. my problem is that the data i need to display in my html table are nested collections of beans like this :

TypeStageBean having:
- get and set attributes,
- Collection of StageBean

and each StageBean have either:
- get and set attributes
- Collection of CourseBean,

and each CourseBean have his get and set attributes

i tried to do this but it doesn't work :
<display:table name="${TypeStageBean}">
<display:column property="numTypeStage" />
<display:column property="nameTypeStage" />
<display:column property="${StageBean.numStage}" />
<display:column property="${StageBean.nameStage}" />
<display:column property="${StageBean.CourseBean.numCourse}" />
<display:column property="${StageBean.CourseBean.nameCourse}" />
</display:table>

i really can't progress so can you help me thankyou.