[Answer]-Recursion in view

finally I came up with this solution:

def getCats(request):
    cats=Category.objects.filter(parent=None)
    s=u'<ul id="red" class="treeview-red">'
    for cat in cats:
        s += hiararchy(cat,True)
    s+=u'</ul>'
    return HttpResponse(simplejson.dumps(s),mimetype='application/json')

def hiararchy(cat,flag):
    if cat.parent and flag:
        return hiararchy(cat.parent,True)
    else:
        if cat.children.count()>0:
            s=u'<li><a href="#" id="'+str(cat.pk)+'" class="cat">%s</a>'%(cat.name)
            for child in cat.children.all():
                s+=u'<ul>%s</li></ul></li>'%(hiararchy(child,False))
            return s
        else:
            return u'<li><a href="#" id="'+str(cat.pk)+'" class="cat">%s</a></li>'%(cat.name) 

pay attention :
1)when a category don’e have parent it means it’s the root node in tree
2)numbering in my example didn’t implement in my code,I needed to replace the name of categories in place of those numbers