diff --git a/trytond/ir/ui/tree.rnc b/trytond/ir/ui/tree.rnc
index a8c1bd3c4a..04f81eeabe 100644
--- a/trytond/ir/ui/tree.rnc
+++ b/trytond/ir/ui/tree.rnc
@@ -1,6 +1,9 @@
 namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
 
-tree = element tree { attlist.tree, field+ }
+tree = element tree { attlist.tree,
+    (field
+     | button)*
+  }
 attlist.tree &=
   [ a:defaultValue = "Unknown" ] attribute string { text }?
 attlist.tree &= attribute on_write { text }?
@@ -49,6 +52,16 @@ attlist.field &=
     | "bottom_to_top"
     | "top_to_bottom"
   }
+button = element button { attlist.button, empty }
+attlist.button &= attribute help { text }?
+attlist.button &=
+  [ a:defaultValue = "Unknown" ] attribute string { text }?
+attlist.button &=
+  [ a:defaultValue = "workflow" ]
+  attribute type { "workflow" | "object" | "action" }?
+attlist.button &= attribute confirm { text }?
+attlist.button &= attribute name { text }
+attlist.button &= attribute states { text }?
 data = element data { attlist.data, xpath+ }
 attlist.data &= empty
 xpath = element xpath { attlist.xpath, any }
diff --git a/trytond/ir/ui/tree.rng b/trytond/ir/ui/tree.rng
index 5f17050cd7..0331df6363 100644
--- a/trytond/ir/ui/tree.rng
+++ b/trytond/ir/ui/tree.rng
@@ -3,9 +3,10 @@
   <define name="tree">
     <element name="tree">
       <ref name="attlist.tree"/>
-      <oneOrMore>
+      <zeroOrMore>
         <ref name="field"/>
-      </oneOrMore>
+        <ref name="button"/>
+      </zeroOrMore>
     </element>
   </define>
   <define name="attlist.tree" combine="interleave">
@@ -150,6 +151,46 @@
       </attribute>
     </optional>
   </define>
+  <define name="button">
+    <element name="button">
+      <ref name="attlist.button"/>
+      <empty/>
+    </element>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <optional>
+      <attribute name="help"/>
+    </optional>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <optional>
+      <attribute name="string" a:defaultValue="Unknown"/>
+    </optional>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <optional>
+      <attribute name="type" a:defaultValue="workflow">
+        <choice>
+          <value>workflow</value>
+          <value>object</value>
+          <value>action</value>
+        </choice>
+      </attribute>
+    </optional>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <optional>
+      <attribute name="confirm"/>
+    </optional>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <attribute name="name"/>
+  </define>
+  <define name="attlist.button" combine="interleave">
+    <optional>
+      <attribute name="states"/>
+    </optional>
+  </define>
   <define name="data">
     <element name="data">
       <ref name="attlist.data"/>