DFS Recursion Space Usage PHP - php

Question

Since arrays are not treated as objects in php, I have to manually reference them in order to recursively fill an array or constantly copy the new created/filled arrays from recursive calls.
"return" myRecursiveFunc() is not an option because that would end the function at the wrong time.
One way: Referencing
public function depthFirstSearchInOrder()
{
$list = []; //otherwise php screams that only variables can be referenced (inside traverseInOrder)
//Otherwise I would have passed an empty [] as second parameter
return traverseInOrder($this->root, $list);
}
function traverseInOrder($node, &$list)
{
if ($node->left) {
traverseInOrder($node->left, $list);
}
$list[] = $node->value;
if ($node->right) {
traverseInOrder($node->right, $list);
}
return $list;
}
Second way: Creating/Copying arrays
public function depthFirstSearchInOrder()
{
return traverseInOrder($this->root);
}
function traverseInOrder($node, $list = [])
{
if ($node->left) {
$list = traverseInOrder($node->left, $list);
}
$list[] = $node->value;
if ($node->right) {
$list = traverseInOrder($node->right, $list);
}
return $list;
}
Doesn't the second way eat up way more space?
I'm creating new Arrays for each recursive call which I'm then copying again in $list.
Or am I just confused at the moment?
If I was to traverse this tree
// 9,
// 4, 20
// 1, 6, 15 170
Using the second way
I would start with 9
Go left and call recursive (because of 4)
Go left and call recursive (because of 1)
I fill my empty array with 1 and return the array [1]
I'm back to value 4 where I now assign to $list = [1] (which now is a copy of [1] NOT a reference, right? So the array [1] still exists afterwards somewhere?
I push 4 in the array [1,4] and go right (because of 6)
I push 6 to the array [1,4,6] and return this array [1,4,6]
I'm back to value 4 where I now assign to $list = [1,4,6] (which now is a copy of [1,4,6] NOT a reference, right? So the array [1,4,6] still exists afterwards somewhere?
And so on and so forth...
Back to my question:
Isn't the second way more space hungry? Or am I just confused at the moment?