diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
index fed243126..bde8af31c 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderElement.java
@@ -61,9 +61,10 @@ import org.navalplanner.business.requirements.entities.DirectCriterionRequiremen
 import org.navalplanner.business.requirements.entities.IndirectCriterionRequirement;
 import org.navalplanner.business.resources.entities.Criterion;
 import org.navalplanner.business.templates.entities.OrderElementTemplate;
+import org.navalplanner.business.trees.ITreeNode;
 
 public abstract class OrderElement extends BaseEntity implements
-        ICriterionRequirable {
+        ICriterionRequirable, ITreeNode<OrderElement> {
 
     private InfoComponent infoComponent = new InfoComponent();
 
@@ -938,4 +939,9 @@ public abstract class OrderElement extends BaseEntity implements
         return infoComponent;
     }
 
+    @Override
+    public OrderElement getThis() {
+        return this;
+    }
+
 }
\ No newline at end of file
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderLineGroup.java b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderLineGroup.java
index 4e62457e4..295a6d6fe 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderLineGroup.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/orders/entities/OrderLineGroup.java
@@ -46,24 +46,26 @@ import org.navalplanner.business.advance.exceptions.DuplicateAdvanceAssignmentFo
 import org.navalplanner.business.advance.exceptions.DuplicateValueTrueReportGlobalAdvanceException;
 import org.navalplanner.business.templates.entities.OrderElementTemplate;
 import org.navalplanner.business.templates.entities.OrderLineGroupTemplate;
-import org.navalplanner.business.trees.ITreeNode;
+import org.navalplanner.business.trees.ITreeParentNode;
 import org.navalplanner.business.trees.TreeNodeOnList;
 
 
 public class OrderLineGroup extends OrderElement implements
-        ITreeNode<OrderElement> {
+        ITreeParentNode<OrderElement> {
 
     private final class ChildrenManipulator extends
-            TreeNodeOnList<OrderElement, OrderLineGroup> {
+            TreeNodeOnList<OrderElement> {
+
+        private final OrderLineGroup parent;
 
         private ChildrenManipulator(OrderLineGroup parent,
                 List<OrderElement> children) {
-            super(parent, children);
+            super(children);
+            this.parent = parent;
         }
 
         @Override
         protected void onChildAdded(OrderElement newChild) {
-            final OrderLineGroup parent = getParent();
             if (parent != null) {
                 SchedulingState schedulingState = newChild
                         .getSchedulingState();
@@ -88,10 +90,30 @@ public class OrderLineGroup extends OrderElement implements
 
         @Override
         protected void setParentIfRequired(OrderElement newChild) {
-            if (getParent() != null) {
-                newChild.setParent(getParent());
+            if (parent != null) {
+                newChild.setParent(parent);
             }
         }
+
+        @Override
+        public ITreeParentNode<OrderElement> getParent() {
+            return OrderLineGroup.this.getParent();
+        }
+
+        @Override
+        public ITreeParentNode<OrderElement> toContainer() {
+            return OrderLineGroup.this.toContainer();
+        }
+
+        @Override
+        public OrderElement toLeaf() {
+            return OrderLineGroup.this.toLeaf();
+        }
+
+        @Override
+        public OrderElement getThis() {
+            return OrderLineGroup.this;
+        }
     }
 
     public static OrderLineGroup create() {
@@ -745,4 +767,9 @@ public class OrderLineGroup extends OrderElement implements
         return OrderLineGroupTemplate.create(this);
     }
 
+    @Override
+    public OrderLineGroup getThis() {
+        return this;
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeNode.java b/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeNode.java
index d4ca373a8..db52c8f9f 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeNode.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeNode.java
@@ -19,23 +19,27 @@
  */
 package org.navalplanner.business.trees;
 
+import java.util.List;
 
 /**
- * Represents an entity that can work as a node at a tree<br />
  * @author Óscar González Fernández <ogonzalez@igalia.com>
+ *
  */
-public interface ITreeNode<T> {
+public interface ITreeNode<T extends ITreeNode<T>> {
 
-    public void add(T newChild);
+    ITreeParentNode<T> getParent();
 
-    public void remove(T existentChild);
+    List<T> getChildren();
 
-    public void replace(T previousChild, T newChild);
+    ITreeParentNode<T> toContainer();
 
-    public void up(T existentChild);
+    T toLeaf();
 
-    public void down(T existentChild);
-
-    public void add(int position, T newChild);
+    /**
+     * Using <a href="http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#FAQ206"
+     * >getThis trick</a>
+     * @return
+     */
+    T getThis();
 
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeParentNode.java b/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeParentNode.java
new file mode 100644
index 000000000..a045fb991
--- /dev/null
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/trees/ITreeParentNode.java
@@ -0,0 +1,41 @@
+/*
+ * This file is part of ###PROJECT_NAME###
+ *
+ * Copyright (C) 2009 Fundación para o Fomento da Calidade Industrial e
+ *                    Desenvolvemento Tecnolóxico de Galicia
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.navalplanner.business.trees;
+
+
+/**
+ * Represents an entity that can work as a node at a tree<br />
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ */
+public interface ITreeParentNode<T extends ITreeNode<T>> extends ITreeNode<T> {
+
+    public void add(T newChild);
+
+    public void remove(T existentChild);
+
+    public void replace(T previousChild, T newChild);
+
+    public void up(T existentChild);
+
+    public void down(T existentChild);
+
+    public void add(int position, T newChild);
+
+}
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/trees/TreeNodeOnList.java b/navalplanner-business/src/main/java/org/navalplanner/business/trees/TreeNodeOnList.java
index e1e479b90..acbac6f5e 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/trees/TreeNodeOnList.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/trees/TreeNodeOnList.java
@@ -23,16 +23,15 @@ import java.util.Collections;
 import java.util.List;
 
 /**
- * Implementation of {@link ITreeNode} that mutates a list <br />
+ * Implementation of {@link ITreeParentNode} that mutates a list <br />
  * @author Óscar González Fernández <ogonzalez@igalia.com>
  */
-public abstract class TreeNodeOnList<T, P> implements ITreeNode<T> {
+public abstract class TreeNodeOnList<T extends ITreeNode<T>> implements
+        ITreeParentNode<T> {
 
     private final List<T> children;
-    private final P parent;
 
-    protected TreeNodeOnList(P parent, List<T> children) {
-        this.parent = parent;
+    protected TreeNodeOnList(List<T> children) {
         this.children = children;
     }
 
@@ -43,10 +42,6 @@ public abstract class TreeNodeOnList<T, P> implements ITreeNode<T> {
         onChildAdded(newChild);
     }
 
-    protected P getParent() {
-        return parent;
-    }
-
     protected abstract void setParentIfRequired(T newChild);
 
     protected abstract void onChildAdded(T newChild);
@@ -92,4 +87,8 @@ public abstract class TreeNodeOnList<T, P> implements ITreeNode<T> {
         onChildAdded(newChild);
     }
 
+    public List<T> getChildren() {
+        return Collections.unmodifiableList(children);
+    }
+
 }