Recommendations

Psychology and mystery. Both involve the complex relationship between a psychiatrist and their client. There is a twist at the end of both.

KMHM is a korean drama, while TGH is a chinese film.

Warning: not much/no romance in The Great Hypnotist. Watch it for the psychology and mystery.

Mystery and multiple people involved. In Kill Me Heal Me, these people are the various personalities of the male lead who has mutiple personality disorder; in Mysterious Summer the mysteries surround different people as it is an anthology series with different leads each ep.

KMHM is a korean drama, while MS a chinese drama. Recommeded chinese drama for people who don't even normally like chinese dramas (I'm one of those people)!

Recommended for fans of original mysteries / not just an ordinary detective story!

Psychology and mystery themed fiction. Both play on the mystery relationship between the leads.

Green Tea is more conversational/dialogue-based, less happens; KMHM has a bigger journey/more happens...but regardless both give their take on psychology.
Green Tea is a chinese film, while Kill Me Heal Me is a korean drama.

There's more similarities between these two besides the very similar poster (lol)...
Both mystery romances, with a chaebol/luxurious life backdrop. The male lead in KMHM must hide his multiple identity disorder from the rich, while the female lead in Mask must hide her true identy as a poor woman from the rich.
Similiar melodrama vibes

Both dramas are about a group of people getting a letter accusing them of having been a part of a murder/suicide which causes them to try and find out who truly killed the person/why the person committed suicide.

A similar sweetness between the romance parts of those two dramas , and very appealing characters in both shows. However, Strong woman has more suspense and dramatic moments , but still very funny and cute parts like in Weightlifting fairy.

Mainly because It has the gorgeous Oh Ji Ho, a dimpled, handsome lead just like in Who's the one, and he's hysterical and sweet as Overweight Karl before he transforms himself into a lean, gorgeous Pro-Golfer. And it has the talented Uhm Jung Hwa as his leading lady upending his life once again.

In both dramas the two main male leads (also childhood friends) are fighting over a female in a rich-poor society circumstances.

Similar plot. Kind-hearted woman saves elderly man, who then decides she deserves his entire fortune. Arrogant grandson wants fortune and after hijenks falls in love with woman.

The plot here also revolves around the act of revenge and also possesses similarities.

If you watched the Lost Tomb (parent story), then I would also recommend the movie version. Also for those who like to watch movies more.

Both are action movies focusing on undercover cops trying to take down crime organizations.

KIM SEULGI! To be honest, nothing common for the plot line except that they are short drama/specials. But if you like Kim Seul GI's sass and cuteness you will definitely enjoy this two drama. Her chemistry with all the actors is like omg omg omg. give her a full drama pls (better with doo joon)

Both dramas are directed and written by the same director/writers and Deep Rooted Tree serves as a direct sequel to Six Flying Dragons.
It follows the story of King Sejong who is Lee Bang Won (King Taejong)'s son (he appears in the last episode of SFD).
Since the two dramas are written by the same writers, many characters are interrelated such as Moohyul and Lee Bangji who are actually made up characters. Also, Mokya, Parkpo, etc. who are supporting characters in Deep Rooted Tree made special appearances in the last episode of SFD.
I highly recommend watching DRT where you can see the older and the more mature Moosa Moohyul.
It's really heart-warming to see recurring characters and you'll end up missing SFD but then again, you'll fall in love with the new ones from DRT.
P.S. Although Shin Sekyung appears in DRT, she takes on the role of a different character :)

Both are about prodigies in surgery & an outstanding doctors.
The main character is also impudent if thats what it takes for a sake of the patients.