Uploading the Video into My Map from Google would be by using YouTube facility, so create your own YouTube channel for uploading the video.
Step 1 : Go to the map
Step 2 : Select the location point which you would like to add a video over
Step 3: From the popup window, click over the camera icon
Step 4: A choose an image or a video pop up window will show up, with a different method to insert image or video.
Note : No any more support upload video to location point directly or through google drive, Just support YouTube Video.