Merge defaults from parent

How can I merge the defaults from the first parent object instead of having to repeat them each time going down the tree?

```js
const validate = ajv.compile({
"type": "object",
"default": {
"url": "abc",
"decimal": 5,
"values": {
"test1": {
"a": 8,
"b": 6
},
"test2": {
"c": 3,
"d": 4
}
}
},
"properties": {
"url": { "type": "string" , "default": "abc" },
"decimals": { "type": "number", "default": 5 }
},
"values": {
"type": "object",
"properties": {
"test1": {
"type": "object",
"default": { "a": 8, "b": 6 },
"properties": {
"a": { "type": "number", "default": 8 },
"b": { "type": "number", "default": 6 }
}
},
"test2": {
"type": "object",
"default": { "c": 3, "d": 4 },
"properties": {
"c": { "type": "number", "default": 3 },
"d": { "type": "number", "default": 4 }
}
}
}
}
});
```
So that it simplifies to this:

```js
const validate = ajv.compile({
"type": "object",
"default": {
"url": "abc",
"decimal": 5,
"values": {
"test1": {
"a": 8,
"b": 6
},
"test2": {
"c": 3,
"d": 4
}
}
},
"properties": {
"url": { "type": "string" },
"decimals": { "type": "number" }
},
"values": {
"type": "object",
"properties": {
"test1": {
"type": "object",
"properties": {
"a": { "type": "number" },
"b": { "type": "number" }
}
},
"test2": {
"type": "object",
"properties": {
"c": { "type": "number" },
"d": { "type": "number" }
}
}
}
}
});
```