oups, not level 5, i meant level 6 !
Push the stone up in to the hole.
Then Free the stone by moving the other stone below it.
Push the free stone up in the Next hole.
Level 6 took some time to find out.
so a short hint for who is stuck.
One stone Need to be in the center lower hole to close the hole on top.
Place it here when the hole is open.
Place the third stone on the lower line to close the hole.
Now push the stone on top of the other stone to the top.
Then move 2 stones to D_5.
Move one stone to D_1 ( so it covers hole at D_5).
Now push the stone at D_5 to the top( D_6 ).
Player now on D_5, move up (D_6).
Stone in hole D_5 now gets out because of stone on D_1. And stone on D_5 opens the path to the exit.