**Core Concept**
Laryngomalacia is a congenital condition characterized by softening of the tissues of the larynx, leading to partial airway obstruction. This condition is often associated with inspiratory stridor, a high-pitched sound heard during inhalation.

**Why the Correct Answer is Right**
Laryngomalacia typically presents in the first few weeks of life, with symptoms often becoming apparent within the first few days. The stridor associated with laryngomalacia is often more pronounced when the infant is in an upright position, as gravity exacerbates the partial airway obstruction. The condition is usually self-limiting and may resolve on its own within the first two years of life, although some cases may require surgical intervention.

**Why Each Wrong Option is Incorrect**
**Option A:** Most common congenital anomaly of larynx - This statement is true. Laryngomalacia is indeed considered the most common congenital anomaly of the larynx in infants.
**Option B:** Stridor disappear on supine position - This statement is false. Stridor associated with laryngomalacia is often more pronounced when the infant is in an upright position, rather than a supine position.
**Option C:** Manifest many weeks after birth - This statement is false. Laryngomalacia typically presents in the first few weeks of life, not many weeks after birth.
**Option D:** It needs no treatment in most of the cases - This statement is true. In most cases, laryngomalacia is self-limiting and requires no treatment, although some cases may require surgical intervention.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of laryngomalacia is the presence of inspiratory stridor, which may be exacerbated by feeding or crying. A high-pitched sound heard during inhalation should prompt further investigation, including a flexible laryngoscopy to confirm the diagnosis.

**Correct Answer: D. It needs no treatment in most of the cases**