C#: variable-width storage class for dissimilar objects without inheritance

[unhappy_mage]

I've got what I think will be either a fairly straightforward or impossible question. I'm trying to implement K-D trees as described here in C#. I've got them mostly working (insertion, searching, that kind of thing) by using a data member of type IComparable[] in a non-parametrized class. However, I'd also like to be able to serialize them to XML. So when I try with the current code, I get an exception because IComparables aren't serializable.

So I see two options.
1) Create a new interface that's both IComparable and IXmlSerializable, and use an array of those as my data member.
2) Make KDTree a parameterized class, with a variable number of different arguments. So I want to be able to instantiate a KDTree<int> and a KDTree<string, double, Image> and anything else, as long as it's comparable and serializable.

Sorry I'm not being very clear; this is all a bit hazy for me as well. Any input you can give is appreciated, and any questions you ask for futher clarification will probably be helpful to both of us.