public Trace swap(Trace other) {
        int level = this.level;
        this.level = other.level;
        other.level = level;

        TraceNode root = this.root;
        this.root = other.root;
        other.root = root;

        return this;
    }
Swap the internals of this with another.

@param other The trace to swap internals with.
@return This, to allow chaining.
messagebus/src/main/java/com/yahoo/messagebus/Trace.java