how to write linq query to get collection of an object

Question

This is my Scenario :

Office which has two branches

branch_1,  branch_2

 

branch_1 has dept_1_1 and dept_1_2

branch_2 has dept_2_1 and dept_2_2 

 

each deprtment has employees.

 

But I need to query through Office  to find name of all the employees in dept_2_2 

 

I would be thankful to help me out to write linq queries.