The steps necessary to create a Tree metadata field filter are

Choose a Meta field group by first opening the "Choose metafield group" window and expanding the tree and selecting the desired tree node.
Choose a tree meta field from the meta field group.
You must add the Field "item_tree_valueid". This is required when the filter is used by Digizuite Media Manager and Digizuite DAM Center.
Choose Comparison Type. When working with tree filters, the comparison type is typically "InList" or "AllInList".
Choose an Input Type. Should probably be "Tree".
Accept the automatically generated ID or write your own.
Optionally choose to make the filter visible.
Optionally add Custom attributes and/or Predetermined values.
Click the "Create" button (the text on the button depends on the selected language).
Click the "Save" (the text on the button depends on the selected language) to persist the changed search.

Creating a Tree filter

Step 3 is very important, because the filter will not work without it, i.e. no results will be returned bu this filter.