Tree leafs reduction

data class Tree<T>(var value: T) {
    var left: Tree<T>? = null
    var right: Tree<T>? = null
}

fun constructSumTree(tree: Tree<Int>?): Tree<Int>? {
    if(tree == null) return null

    reduceLeafs(tree)
    return tree
}

fun reduceLeafs(tree: Tree<Int>): Int {
    with(tree){
    if(left == null && right == null) {
        println("Leafs reached")
        val temp = value
        value = 0
        return temp
    }

    val leftValue = if(left == null) 0 else reduceLeafs(left!!)
    val rightValue = if(right == null) 0 else reduceLeafs(right!!)

    value += leftValue + rightValue


    println("New value set to value")
    return value
    }
}