I'm trying to recreate this:

I've tried using flex-box and grid, but, no success so far.
You will find my CSS code below to illustrate what I've tried, but it doesn't seem to be the most efficient way.
I'm looking forward to any tips or solutions you might give me.
.parent {
display: grid;
grid-template-columns: repeat(6, 1fr);
grid-template-rows: repeat(5, 1fr);
grid-column-gap: 0px;
grid-row-gap: 0px;
}
.div1 { grid-area: 1 / 2 / 2 / 4; }
.div2 { grid-area: 1 / 4 / 2 / 5; }
.div3 { grid-area: 1 / 5 / 2 / 6; }
.div4 { grid-area: 2 / 2 / 3 / 4; }
.div5 { grid-area: 2 / 4 / 3 / 5; }
.div6 { grid-area: 2 / 5 / 3 / 6; }
.div7 { grid-area: 3 / 2 / 4 / 4; }
.div8 { grid-area: 3 / 4 / 4 / 5; }
.div9 { grid-area: 3 / 5 / 4 / 6; }
.div10 { grid-area: 4 / 2 / 5 / 4; }
.div11 { grid-area: 4 / 4 / 5 / 5; }
.div12 { grid-area: 4 / 5 / 5 / 6; }
.div13 { grid-area: 5 / 2 / 6 / 4; }
.div14 { grid-area: 5 / 4 / 6 / 5; }
.div15 { grid-area: 5 / 5 / 6 / 6; }