Create a new chart and choose the Pivot Table as chart type. Add your products field as the first dimension and your weeks field as second dimension. Also add an expression that calculates something, for example sum(Sales). On the Presentation tab of the properties screen check the Partial Sums option for both dimensions. Under Subtotals you can choose if you want subtotals at the top or bottom (for a row dimension that means left or right). You may want to check the option Always Fully Expanded too. The weeks field will be the second column, so you'll have to drag it to above the expression column. This can be a bit tricky. When you see a horizontal blue arrow appear you can let go and the weeks field should be in the right place.
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