LeetCode: Intersection of two arrays ii C#

https://leetcode.com/problems/intersection-of-two-arrays-ii/

Please review for performance, I am having a problem with using TryGetValue, if someone can explain how this can be used in here.

Given two arrays, write a function to compute their intersection.

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]
Output: [2,2]
Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [4,9]
Note:

Each element in the result should appear as many times as it shows in both arrays. The result can be in any order.

using System.Collections.Generic;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace ArrayQuestions
{
    /// <summary>
    /// https://leetcode.com/problems/intersection-of-two-arrays-ii/
    /// </summary>
    [TestClass]
    public class IntersectionOfTwoArraysii
    {
        [TestMethod]
        public void IntersectionOfDouble2Test()
        {
            int[] nums1 = {1, 2, 2, 1};
            int[] nums2 = {2, 2};
            CollectionAssert.AreEqual(nums2, Intersect(nums1,nums2));
        }

        public int[] Intersect(int[] nums1, int[] nums2)
        {
            if (nums1.Length > nums2.Length)
            {
                return Intersect(nums2, nums1);
            }
            Dictionary<int, int> nums1Count = new Dictionary<int, int>();
            List<int> res = new List<int>();
            foreach (var num in nums1)
            {
                if (!nums1Count.ContainsKey(num))
                {
                    nums1Count.Add(num,1);
                }
                else
                {
                    nums1Count[num]++;
                }
            }

            foreach (var num in nums2)
            {
                if (nums1Count.ContainsKey(num) && nums1Count[num] > 0)
                {
                    res.Add(num);
                    nums1Count[num]--;
                }
            }

            return res.ToArray();
        }
    }
}