filesets-tree-max-level

filesets-tree-max-level is a variable defined in `filesets.el'.
Its value is

3

Documentation:
Maximum scan depth for directory trees.
A :tree fileset is defined by a base directory the contents of which
will be recursively added to the menu. `filesets-tree-max-level' tells up
to which level the directory structure should be scanned/listed,
i.e. how deep the menu should be. Try something like

("HOME -- only one level"
(:tree "~" "^[^.].*[^~]$")
(:tree-max-level 1)
(:filter-dirs-flag t))
("HOME -- up to 3 levels"
(:tree "~" "^[^.].*[^~]$")
(:tree-max-level 3)
(:filter-dirs-flag t))

and it should become clear what this option is about. In any case,
including directory trees to the menu can take a lot of memory.

You can customize this variable.