SCSS

HTML

<nav>
  <div>A</div>
  <div>B</div>
  <div>C</div>
  <div>D</div>
  <div>E</div>
  <div>F</div>
</nav>

SCSS

nav {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  
  height: 250px;
  width: 150px;
  border: 1px solid red;
  
  & > div:nth-child(5),
	& > div:nth-child(6) {
	  
    margin-top: auto;
    
	}
}

div {
  display: flex;
  justify-content: center;
  border: 1px solid blue;
  width: 100%;
}