Suppose, I am using a table with fields A and B. A has the main tasks
and B has the sub tasks (I know I could use different tables for
one-to-many, but it is just for an example). Data in the table may be
like:

Record1: A=a, B=x
Record2: A=a, B=y
Record3: A=a, B=z
Record4: A=b, B=p
Record5: A=b, B=q
and so on...

I want to use the table in a form. But the problem is that- I want to
fit it like grouping on A field that initially there will be only
distinct A values and as when I double click the A, then A will be
expanded to its corresponding values (records)of B-Like tree view effect in
a table in the form.

Is there any sample database at any site from where I can get help? OR,
do you have any code sample/idea how I can do this?

create a select query that will pull the information out based on A... then switch to sql view and save the statement... the first word of it will be SELECT... add the word DISTINCT behind it and you should get the result your looking for.