**Core Concept**
The gluteus maximus is a large, superficial muscle of the buttock that plays a key role in hip extension and external rotation. Its insertion is an essential anatomical landmark for various clinical procedures and surgical approaches.

**Why the Correct Answer is Right**
The gluteus maximus muscle is inserted onto the iliotibial (IT) tract, which is a fibrous structure that extends from the iliac crest to the tibia. The IT tract serves as a common insertion point for several muscles, including the gluteus maximus, tensor fasciae latae, and the sartorius. The insertion onto the IT tract allows the gluteus maximus to effectively extend and rotate the hip joint.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as the gluteus maximus does not insert onto the greater trochanter of the femur, which is the site of insertion for the gluteus medius and minimus muscles.
* **Option B:** This option is incorrect as the gluteus maximus does not insert onto the ischial tuberosity, which is the site of insertion for the hamstring muscles.
* **Option C:** This option is incorrect as the gluteus maximus does not insert onto the femoral condyles, which are the sites of insertion for the quadriceps and hamstring muscles.

**Clinical Pearl / High-Yield Fact**
The IT tract is a significant anatomical landmark for various clinical procedures, including the iliotibial band friction syndrome, which occurs when the IT tract rubs against the lateral femoral condyle, causing pain and inflammation.

**Correct Answer: D. Iliotibial tract**