Using Tree in CAF

Hi,
I have a web service, we called it ws which gave parent/childen relation.
This web service as result given IDParent, IDChildren, ChildrenTitle.

I create a ListTreeContentProvider in my Bindings (we called it provider) and I set it like that :
Row variable = p
Array Source = “#{ws.result.result}”
Row ID expression = “#{p.IDChildren}”
Row ID Parent = “#{p.IDParent}”

my Action initialise has an Action :
ws.Refresh

And I Create a dataTree with the following attributes :
Value = “#{provider}”
Variable name = “row”

And I have a treeToogle on it with a text with the value :"#{row.ChildrenTitle}"

But it doesn’t work. I have no mistake but the tree is empty despite the web service gave values.