Most of the navigation tree we are familiar with, it’s the vertical tree pattern. Of course, you also have seen the horizontal tree before, like Mac Finder or File explorer.
Horizontal tree works well when you have one to many relationship that needs to be represented in a hierarchy, but for many to many, it doesn’t work well.
Here I have created a solution for the horizontal tree for many to many relationship, in other words when you need to select multiple items from each node on the hierarchy.
Giving individual box for each level of the hierarchy, and on the second level, you see a combined result grouped by the previous level (node).