Disable a move down in Google Charts Treemap

[KEM]

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I am using the Google-Charts Treemap to display a very large number of nodes. The default behavior is to move down the tree when a user left-clicks a node and to move back up the tree when a user right-clicks the graph. The right-clicks redraw the chart for each click. The redraw is very slow because of the large number of nodes. How to disable the node move down function without disabling the mouse click event? How to improve the performance of treemap draw? Thanks