Cây này rất nhỏ.

• cây = tree or plant, depending on context
• này = this
• rất = very
• nhỏ = small

So the structure is basically:

noun + this + very + adjective

Vietnamese often builds simple descriptive sentences this way.

In Vietnamese, demonstratives like này (this) usually come after the noun:

• cây này = this tree / this plant
• nhà này = this house
• người này = this person

This is different from English, where this comes before the noun.

So:

• English: this tree
• Vietnamese: cây này

Vietnamese often does not use a copula like English is/are when describing something with an adjective.

So instead of saying something like This tree is very small with a separate word for is, Vietnamese simply says:

Cây này rất nhỏ
literally: tree this very small

This is completely normal Vietnamese sentence structure.

Rất means very. It strengthens the adjective nhỏ (small).

• Cây này nhỏ. = This tree is small.
• Cây này rất nhỏ. = This tree is very small.

You do not have to use rất. The sentence still works without it. It just becomes less strong.

Also, in beginner Vietnamese, rất + adjective is one of the most common ways to describe something.

It can mean either tree or plant, depending on context.

For example:

• In some situations, cây này would naturally mean this tree
• In others, especially indoors or around flowers/potted greenery, it may mean this plant

Also, cây is used as a classifier for some long, stick-like objects, but in this sentence it is most naturally understood as the main noun: tree/plant.

Yes. That is completely correct.

• Cây này nhỏ. = This tree/plant is small.
• Cây này rất nhỏ. = This tree/plant is very small.

Using rất just adds emphasis. Learners sometimes think a degree word is always required before an adjective, but in everyday Vietnamese, nhỏ can stand on its own just fine.

Because Vietnamese commonly puts the adjective after the subject in this kind of sentence.

Pattern:

• [thing] + [optional demonstrative] + [degree word] + [adjective]

So:

• Cây này rất nhỏ
• Nhà này rất đẹp = This house is very beautiful
• Con mèo này rất dễ thương = This cat is very cute

This is different from English, where adjectives often come before nouns inside noun phrases, like a small tree. But here the sentence is not small tree; it is this tree is very small.

They are similar, and both can mean small, but they are not always identical.

• nhỏ is a broad, common word for small
• bé also means small/little, but it often feels more natural for people, children, or things spoken of in a more affectionate or cute way

For a tree or plant, nhỏ is the safest and most neutral choice:

• Cây này rất nhỏ sounds natural

Using bé here is less standard unless the speaker is being cute or expressive.

A rough guide:

• cây → sounds a bit like guy but with a different starting consonant and Vietnamese tone
• này → roughly like nye
• rất → short, clipped syllable; the final t is unreleased
• nhỏ → roughly like nyaw with the Vietnamese hỏi tone

One important point: Vietnamese is tonal, so correct tones matter a lot. In this sentence, all four words have their own tone pattern, and changing the tone can change the meaning or make the word hard to understand.

No, that would not be normal Vietnamese.

The natural order is:

Cây này rất nhỏ

The demonstrative này comes after the noun, not before it. So keep cây này together as the phrase meaning this tree / this plant.