how to display only part of the TreeGrid

hello,
have you any idea how to display only part of the TreeGrid (change the root of the TreeGrid )
Example:
Root
+M1
-M1_01
-M1_02
+M2
-M2_01
-M2_02
-M2_03
+M3
+M4

and i want to display the tree from the element M2:
+M2
-M2_01
-M2_02
-M2_03
+M3
+M4

Thank you in advance