To select an individual product you can use the Items dropdown. Before selecting a product you have to select the level of aggregation. Once you have selected a level of aggregation the corresponding products list gets populated in the dropdown below. You can scroll through the dropdown and select the product or type the product code or name to narrow your selection. Once you have selected the product use the > button to move the product to the selection panel. You can repeat the same steps for different/same level of aggregation to add more products
Next: Selecting products from Tree
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The World Bank, 2010