I am writing in swift 3.0

I have this code which gives me the warning result of the call is unused

public override init(){
    super.init()
}
            
public init(annotations: [MKAnnotation]){
    super.init()
    addAnnotations(annotations:  annotations)        
}
            
public func setAnnotations(annotations:[MKAnnotation]){
    tree = nil
    addAnnotations(annotations: annotations)
}
            
public func addAnnotations(annotations:[MKAnnotation]){
    if tree == nil {
        tree = AKQuadTree()
    }
                
    lock.lock()
    for annotation in annotations {
// The warning occurs at this line
        tree!.insertAnnotation(annotation: annotation)
    }
    lock.unlock()
}

I have tried using this method in another class but it still gives me the error the code for insert Annotation is above

func insertAnnotation(annotation:MKAnnotation) -> Bool {
    return insertAnnotation(annotation: annotation, toNode:rootNode!)
}
        
func insertAnnotation(annotation:MKAnnotation, toNode node:AKQuadTreeNode) -> Bool {
            
    if !AKQuadTreeNode.AKBoundingBoxContainsCoordinate(box: node.boundingBox!, coordinate: annotation.coordinate) {
        return false
    }
            
    if node.count < nodeCapacity {
        node.annotations.append(annotation)
        node.count += 1
        return true
    }
            
    if node.isLeaf() {
        node.subdivide()
    }
            
    if insertAnnotation(annotation: annotation, toNode:node.northEast!) {
        return true
    }
            
    if insertAnnotation(annotation: annotation, toNode:node.northWest!) {
        return true
    }
            
    if insertAnnotation(annotation: annotation, toNode:node.southEast!) {
        return true
    }
            
    if insertAnnotation(annotation: annotation, toNode:node.southWest!) {
        return true
    }
    
    return false
}

I have tried many methods but just doesn’t work but in swift 2.2 it works fine any ideas why this is happening?