.form-item-field-source-und .form-checkboxes .form-type-checkbox,
.term-reference-tree ul.term-reference-tree-level ul.term-reference-tree-level > li {
    width: 25%;
}
.form-item-field-source-und .form-checkboxes,
.term-reference-tree ul.term-reference-tree-level ul.term-reference-tree-level {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
}

.term-reference-tree ul.term-reference-tree-level ul.term-reference-tree-level ul.term-reference-tree-level > li {
    width: 100%;
}

.term-reference-tree > ul.term-reference-tree-level > li {
    margin-bottom: 25px;
}