Add TreeGrid#getHierarchyColumn

server/src/main/java/com/vaadin/ui/TreeGrid.java

@@ -252,6 +252,16 @@ public class TreeGrid<T> extends Grid<T>
         super.setDataProvider(dataProvider);
     }
 
+    /**
+     * Get the currently set hierarchy column.
+     *
+     * @return the currently set hierarchy column, or {@code null} if no column
+     *         has been explicitly set
+     */
+    public Column<T, ?> getHierarchyColumn() {
+        return getColumn(getState(false).hierarchyColumnId);
+    }
+
     /**
      * Set the column that displays the hierarchy of this grid's data. By
      * default the hierarchy will be displayed in the first column.