that requires years of training and centuries of dedication.

At the 2012 international bonsai convention,

a tree was on sale for 100 million yen,

just under a million dollars.

And many more of these trees

are considered completely priceless.

So what is it that makes bonsai so expensive?

Bonsai is the art of dwarfing a regular tree

to create a perfect miniature representation of nature

in a small pot.

It has a long history.

Originating in China,

the practice of creating tiny trees

and landscapes appeared as far back as the sixth century.

The tree's growth is restricted

by years of pruning, wiring, repotting, and grafting,

and the plants need to be checked on

and often watered every day.

The skills required to grow these trees

plays a huge part in their value.

They're often bent and twisted into shape,

positioned around rocks,

or even placed with other trees to simulate a tiny forest.

Many of these techniques require years to master,

and any errors made

can result in permanently ruining the shape

or even killing a plant that has been growing for centuries.

Chiako Yamamoto is a fourth-generation bonsai master

based in central Japan.

She's been creating and selling bonsai

for the last 51 years,

and one of the hardest skills to master

when growing these plants is patience.

The time and devotion this process requires

is unlike almost any other form of artwork.

While the work is almost a form of sculpture,

the plants are living things

and will always react in their own way.

The extraordinary time this process takes means

that just aren't that many trees around.

Some of the most valuable bonsai are over 800 years old,

and so the supply isn't going to increase anytime soon.

Other factors can contribute to the cost.

The bonsai pots and the tools used are often handmade

and can cost thousands of dollars themselves.

Certain types of tree are also harder to grow

or require certain techniques and may fetch a higher price.

But, more than anything, these trees are works of art

valued for their beauty and the vision of the artist.