A gerund is the -ing form of a verb used as a noun.
In this sentence, the subject is the action of rising early in the morning, so we need the gerund form rising.
Why the other options are wrong?
❌ to rise → Infinitive form, not a gerund.
❌ rise → Base form of the verb; it cannot function as the required noun phrase here.
❌ having risen → Perfect participle; it emphasizes a completed action and is not appropriate as the simple subject of the sentence.
