Appearance of sub Accounts when put curser on main account

Hi there

I use combobox on userform to view list of accounts, some accounts they contain sub accounts..........

how to make these sub accounts appear while i put the curser on an account that contains sub accounts under it ?

For Example :
I need to put the curser on the Expense Account(Main Account) so the sub list should appear to show the sub accounts (what are the expenses)
i.e
Expenses........wages
.........Tax
.........Maintinance
.........Fuel

Any idea ?

any idea so far ????