Create a class of hierarchy list from list using LINQ

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LINQ

Hi i have the below data , employee column consider as parent and each employee have invoice as child and each invoice have invoicedetails as subchild. i have binded this data into a list of class. now i want create hierarchy list from this list using LINQ

parent--->child--->subchild
Employee--->Invoice--->InvoiceDetails

List Data:

Employee invoice InvoiceDetails jan feb Mar Apr
E1 I1 ID1 1 2 10 5
E1 I1 ID2 1 3 11 6
E1 I1 ID3 1 4 12 7
E1 I2 ID1 1 5 13 8
E1 I2 ID2 1 6 14 9
E1 I2 ID3 1 7 15 10
E2 I1 ID1 1 8 16 11
E2 I1 ID2 1 10 17 12

Output :

E1
--I1
------ID1 1 2 10 5
------ID2 1 3 11 6
------ID3 1 4 12 7
--I2
------ID1 1 5 13 8
------ID2 1 6 14 9
------ID3 1 7 15 10
E2
--I1
---------ID1 1 8 16 11
---------ID2 1 10 17 12

What I have tried:

i have tried for 2 label of class but don't have idea for 3 label of hierarchy

var query = (from f in CustomerAllocation1
                         select new Field
                         {
                             FieldId = f.FieldId,
                             //EmployeeId = e.EmployeeId,


                             //InvoiceDetailsListRows.ForEach(z => z.ChildCount = items.Count(x => x.ParentId == z.Id)),
                             Children = (from c in CustomerAllocation
                                         where c.FieldId == f.FieldId
                                         select new Customer
                                         {
                                             FieldId = f.FieldId,
                                             CustomerId = c.CustomerId,

                                             jan = c.jan,
                                             feb = c.feb,
                                             mar= c.mar
                                             april= c.april

}).tolist()
}).tolist()