How should I setup a UI for editing a binary tree? [closed]

Question

I need to allow the user to create an binary tree. I have a Backbone Model populating properly from the database, the problem I am stuck on is how do I setup the ui elements in a way that is fairly easy to use?

The general idea is I want to create a boolean expression that contains logic and tokens. The tokens will be replaced later at runtime with appropriate model data when the expression is evaluated.

You end up with a final expression like this:

((({Claim.State})=(TX))||(({Claim.PolicyState})!=(UT)))

Ie, Evaluate to true if the State = TX or the Policy State is not UT

Each expression can be a terminating node, and will have a value, or will have no value, and the left and right will point to the next respective expressions and an Operator

The database structure looks something like this:

1. State Check: Left: 2 Right: 3 Operator: OR
2. State is TX: Left: 4 Right 5 Operator: Equals
3. State not UT: Left: 6 Right 7: Operator: Not
4. Claim State: Left: nil Right: nil Value: {Claim.State}
5. Texas Literal: Left: nil Right: nil Value: "TX"
6. Policy State: Left: nil Right: nil Value: {Claim.PolicyState}
7. Utah Literal: Left: nil Right: nil Value: "UT"

I am imaging something like for the Above expression, making a panel with 3 select lists, and a Label above it:

---------------------------------------------------------------- 
Name: |State Check|                     [.] Value [0] Expression
            Left (Edit/New)   Operator Right (Edit/New) 
Expression: [ State is TX ]   [ Or ]   [ State is not UT ] 
(Save)
----------------------------------------------------------------

At this point I'm stuck. What should happen when say, the user wants to edit the left hand value? Do I open a new popup window to rerender the same form, just starting with 2 instead of 1 for the starting expression key?

Should I replace the existing form with the new values, and somehow keep track of where the user is in reference to the starting expression?

Maybe slide a new editor panel down below the current?

A few extra details:

1. My users will be semi technical, the binary expression concept is understood, I just need a clean way to express the ideas.

2. I'll be using a combination of backbone.js and jQuery with Underscore templates

3. There is a c#/MVC3/sql08 backend

What do you think ?