diff --git a/system/project.py b/system/project.py
index 2d707b4..5fa7f99 100644
--- a/system/project.py
+++ b/system/project.py
@@ -48,22 +48,25 @@ class Project:
     def get_data_iter(self, obj):
         """Retuns an iterator to data."""
         retval = [None]
+        if obj:
+            # add data below first function data input
+            obj=obj[0]
+
         def is_obj(m, p, i, d):
             if obj == m.get_value(i, 2):
                 d.append(i)
                 return True
-
+                
         self.data_tree.foreach(is_obj, retval)
         return retval[-1]
 
-    def add_data(self, parent, data, fun='Function'):
+    def add_data(self, parents, data, fun='Function'):
         """Adds a set of data and plots to the navigator.
 
         This method is usually called after a Function in a workflow
         has finished and returns its output."""
         
-        parent_iter = self.get_data_iter(parent)
-
+        parent_iter = self.get_data_iter(parents)
         it = self.data_tree_insert(parent_iter, fun, None, "grey","black")
 
         for d in data: