Euphorbia trigona goes by several common names. Cathedral cactus, African milk tree, and Abyssinian euphorbia all refer to this plant. African milk trees grow naturally in Central Africa, where it may be used as a shrub or hedge in the arid climate. As a houseplant in cultivation, they tend to stay smaller and has the potential to grow more slowly than in the wild.
Place your Euphorbia in an area where it will receive plenty of light, such as under a grow light or in a southern facing window and water only when the soil is completely dry. If you plan on moving this outside during the summer months, remember to slowly adjust it to full sun conditions by leaving it in partial shade to begin, then slowly giving it more sun as time goes on until it is in full sun. This is to prevent damaging sunburn and sun scorch.
Do this, and you will see your African Milk Tree begin to branch and keep the stunning variegation!