The Categories[Set] command associates a top-level menu entry with a given category.

with(ContextMenu[CurrentContext]);

$\left[\mathrm{Categories}\,\mathrm{Copy}\,\mathrm{Entries}\,\mathrm{EntryGenerators}\,\mathrm{HandleExpression}\,\mathrm{Queries}\right]$

In this example, "Language Conversions" and "Test Primality" have distinct categories.  Therefore, if a context-sensitive menu, which includes both categories, is generated, it should insert a delimiter between them.

Categories[Set]("Language Conversions", "Category 1");

Categories[Set]("Test Primality", "Category 2");

Entries[Add]("Test Primality",  "isprime(%EXPR)", integer);

$432$

Entries[Add]("To Matlab",  "CodeGeneration[Matlab](%EXPR)", algebraic, submenu=["Language Conversions"]);

$836$

Entries[Add]("To Fortran", "CodeGeneration[Fortran](%EXPR)", algebraic, submenu=["Language Conversions"]);

$853$