Collections selections

Hi All,
I am stuck with having to develop a data structure to hold parsed data from an XML file. I am new to collections and I have a scenario like below where I can have a single key or multiple keys, each containing specific values. I am not sure what to use to store this data. I realize this may be a simple question for some, but I am new to this and can't seem to wrap my head around it....thx

Scenario 1: single key, single value
single key
key field (tracking number)------key values (12345)

Scenario 2: single key, multiple values
key field (tracking number)------key values (12345)
------key values (abc1234)
Scenario 3: multiple key, single values
key field (tracking number)------key values (12345)
key field (shipement)------------key values (1)

Scenario 4: multiple key, multiple values
key field (tracking number)------key values (12345)
------key values (abc1234)
key field (shipement)------------key values (1)
------key values (0)

I need a structure that will hold all these forms and be able to be rapidly searched. I suspect a Collection of some kind, but not sure where to go fro here. Any help is greatly appreciated....
Thanks,
jim