Windows 10 doesn’t really provide a way to customize the density of Start tiles, but with version 1511 you can now display more tiles in each Start column.
By default, Start displays tiles in columns that can support up to three medium-sized tiles per column.
But you can configure Start so that each column supports four medium-sized tiles. To do so, open Settings and navigate to Personalize, Start. Then, enable the option “Show more tiles.” When you re-open Start, you’ll see a medium tile-sized gap has been added to each column.
From here, you can simply drag in the tiles you wish to use.