Show dialog box on Add to Bar for already existig window

As we can Add any window on Navigation Bar by click on Add to Bar, if a window already exist on Navigation Bar and we again add that window by clicking on "Add to Bar" then it should display a dialog-box as "This window already Added" ; At the moment it raise an error !

DB.executeUpdate: INSERT INTO AD_TreeBar (AD_Tree_ID,AD_User_ID,Node_ID, AD_Client_ID,AD_Org_ID, IsActive,Created,CreatedBy,Updated,UpdatedBy)VALUES (10,100,53237,11,11,'Y',CURRENT_TIMESTAMP,100,CURRENT_TIMESTAMP,100) [null] [11]
org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "ad_treebar_pkey"; State=23505; ErrorCode=0
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2062)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1795)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:479)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:367)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeUpdate(AbstractJdbc2Statement.java:321)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:105)
at sun.reflect.GeneratedMethodAccessor25.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.compiere.db.StatementProxy.invoke(StatementProxy.java:100)
at $Proxy0.executeUpdate(Unknown Source)
at org.compiere.util.DB.executeUpdate(DB.java:1014)
at org.compiere.util.DB.executeUpdate(DB.java:917)
at org.compiere.util.DB.executeUpdate(DB.java:903)
at org.compiere.grid.tree.VTreePanel.barDBupdate(VTreePanel.java:961)
at org.compiere.grid.tree.VTreePanel.barAdd(VTreePanel.java:813)
at org.compiere.grid.tree.VTreePanel.actionPerformed(VTreePanel.java:795)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)

===========> DB.saveError: DBExecuteError - ERROR: duplicate key value violates unique constraint "ad_treebar_pkey" [11]