Difference in performance when inverting a binary tree

Question

Now I have two solutions. But I can’t understand why the first solution is faster than the second solution.

First decision

public class Solution {
  public TreeNode invertTree(TreeNode root) {
        if(root == null)
            return root;

        if(root.left==null && root.right==null)
            return root;

        TreeNode temp = null;
        root.left = invertTree(root.left);
        root.right =invertTree(root.right);
        temp = root.left;
        root.left = root.right;
        root.right = temp;
        return root;
    }
}

Second solution

public class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null)
            return null;

        if (root.left == null && root.right == null)
            return root;

        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        invertTree(root.left);
        invertTree(root.right);
        return root;
    }
}

Answer 1

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